Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $188.33   7.792%   $203.0047   $203.00   $203.00   $203.00  
  Purchase #2 $175.26   6.608%   $186.8412   $186.84   $186.85   $186.80  
  Purchase #3 $243.70   9.670%   $267.2658   $267.27   $267.25   $267.30  
  Purchase #4 $219.94   12.225%   $246.8277   $246.83   $246.85   $246.80  
  Purchase #5 $177.47   13.388%   $201.2297   $201.23   $201.25   $201.20  
  Purchase #6 $197.46   11.706%   $220.5747   $220.57   $220.55   $220.60  
  Purchase #7 $153.77   13.115%   $173.9369   $173.94   $173.95   $173.90  
  7 purchase totals = $1,355.93       $1,499.6807   $1,499.68   $1,499.70   $1,499.60