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 $244.56   5.287%   $257.4899   $257.49   $257.50   $257.50  
  Purchase #2 $89.58   6.457%   $95.3642   $95.36   $95.35   $95.40  
  Purchase #3 $125.74   4.629%   $131.5605   $131.56   $131.55   $131.60  
  Purchase #4 $155.75   11.450%   $173.5834   $173.58   $173.60   $173.60  
  Purchase #5 $60.86   6.399%   $64.7544   $64.75   $64.75   $64.80  
  Purchase #6 $158.58   6.765%   $169.3079   $169.31   $169.30   $169.30  
  Purchase #7 $108.84   8.533%   $118.1273   $118.13   $118.15   $118.10  
  7 purchase totals = $943.91       $1,010.1876   $1,010.18   $1,010.20   $1,010.30