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 $243.84   9.763%   $267.6461   $267.65   $267.65   $267.60  
  Purchase #2 $110.82   13.322%   $125.5834   $125.58   $125.60   $125.60  
  Purchase #3 $80.57   12.678%   $90.7847   $90.78   $90.80   $90.80  
  Purchase #4 $103.51   12.226%   $116.1651   $116.17   $116.15   $116.20  
  Purchase #5 $120.71   9.707%   $132.4273   $132.43   $132.45   $132.40  
  Purchase #6 $117.31   3.230%   $121.0991   $121.10   $121.10   $121.10  
  Purchase #7 $103.40   8.594%   $112.2862   $112.29   $112.30   $112.30  
  7 purchase totals = $880.16       $965.9919   $966.00   $966.05   $966.00