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 $223.72   10.515%   $247.2442   $247.24   $247.25   $247.20  
  Purchase #2 $243.65   3.240%   $251.5443   $251.54   $251.55   $251.50  
  Purchase #3 $59.60   4.351%   $62.1932   $62.19   $62.20   $62.20  
  Purchase #4 $25.47   7.506%   $27.3818   $27.38   $27.40   $27.40  
  Purchase #5 $209.38   13.665%   $237.9918   $237.99   $238.00   $238.00  
  Purchase #6 $242.45   9.677%   $265.9119   $265.91   $265.90   $265.90  
  Purchase #7 $42.73   13.226%   $48.3815   $48.38   $48.40   $48.40  
  7 purchase totals = $1,047.00       $1,140.6487   $1,140.63   $1,140.70   $1,140.60