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 $217.35   13.378%   $246.4271   $246.43   $246.45   $246.40  
  Purchase #2 $242.92   3.306%   $250.9509   $250.95   $250.95   $251.00  
  Purchase #3 $133.28   9.839%   $146.3934   $146.39   $146.40   $146.40  
  Purchase #4 $159.48   6.295%   $169.5193   $169.52   $169.50   $169.50  
  Purchase #5 $79.42   9.447%   $86.9228   $86.92   $86.90   $86.90  
  Purchase #6 $242.45   10.755%   $268.5255   $268.53   $268.55   $268.50  
  Purchase #7 $33.33   5.817%   $35.2688   $35.27   $35.25   $35.30  
  7 purchase totals = $1,108.23       $1,204.0078   $1,204.01   $1,204.00   $1,204.00