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 $91.74   11.868%   $102.6277   $102.63   $102.65   $102.60  
  Purchase #2 $63.74   5.701%   $67.3738   $67.37   $67.35   $67.40  
  Purchase #3 $125.68   3.791%   $130.4445   $130.44   $130.45   $130.40  
  Purchase #4 $174.94   4.369%   $182.5831   $182.58   $182.60   $182.60  
  Purchase #5 $41.26   12.220%   $46.302   $46.30   $46.30   $46.30  
  Purchase #6 $133.59   5.536%   $140.9855   $140.99   $141.00   $141.00  
  Purchase #7 $204.97   11.485%   $228.5108   $228.51   $228.50   $228.50  
  7 purchase totals = $835.92       $898.8274   $898.82   $898.85   $898.80