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 $65.96   11.766%   $73.7209   $73.72   $73.70   $73.70  
  Purchase #2 $219.48   9.190%   $239.6502   $239.65   $239.65   $239.70  
  Purchase #3 $112.75   8.180%   $121.973   $121.97   $121.95   $122.00  
  Purchase #4 $94.86   7.722%   $102.1851   $102.19   $102.20   $102.20  
  Purchase #5 $237.76   9.221%   $259.6838   $259.68   $259.70   $259.70  
  Purchase #6 $17.93   6.456%   $19.0876   $19.09   $19.10   $19.10  
  Purchase #7 $53.56   7.549%   $57.6032   $57.60   $57.60   $57.60  
  7 purchase totals = $802.30       $873.9038   $873.90   $873.90   $874.00