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 $228.38   11.827%   $255.3905   $255.39   $255.40   $255.40  
  Purchase #2 $168.30   5.198%   $177.0482   $177.05   $177.05   $177.00  
  Purchase #3 $70.74   4.590%   $73.987   $73.99   $74.00   $74.00  
  Purchase #4 $182.94   13.110%   $206.9234   $206.92   $206.90   $206.90  
  Purchase #5 $169.78   6.680%   $181.1213   $181.12   $181.10   $181.10  
  Purchase #6 $65.48   8.701%   $71.1774   $71.18   $71.20   $71.20  
  Purchase #7 $72.56   8.455%   $78.6949   $78.69   $78.70   $78.70  
  7 purchase totals = $958.18       $1,044.3427   $1,044.34   $1,044.35   $1,044.30