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 $225.56   6.862%   $241.0379   $241.04   $241.05   $241.00  
  Purchase #2 $82.29   6.179%   $87.3747   $87.37   $87.35   $87.40  
  Purchase #3 $118.42   9.299%   $129.4319   $129.43   $129.45   $129.40  
  Purchase #4 $161.26   5.228%   $169.6907   $169.69   $169.70   $169.70  
  Purchase #5 $75.72   6.278%   $80.4737   $80.47   $80.45   $80.50  
  Purchase #6 $9.78   3.571%   $10.1292   $10.13   $10.15   $10.10  
  Purchase #7 $46.39   7.459%   $49.8502   $49.85   $49.85   $49.90  
  7 purchase totals = $719.42       $767.9883   $767.98   $768.00   $768.00