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 $96.65   5.161%   $101.6381   $101.64   $101.65   $101.60  
  Purchase #2 $118.54   6.852%   $126.6624   $126.66   $126.65   $126.70  
  Purchase #3 $181.69   11.146%   $201.9412   $201.94   $201.95   $201.90  
  Purchase #4 $168.35   12.348%   $189.1379   $189.14   $189.15   $189.10  
  Purchase #5 $59.76   4.637%   $62.5311   $62.53   $62.55   $62.50  
  Purchase #6 $11.34   13.103%   $12.8259   $12.83   $12.85   $12.80  
  Purchase #7 $50.44   10.569%   $55.771   $55.77   $55.75   $55.80  
  7 purchase totals = $686.77       $750.5076   $750.51   $750.55   $750.40