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 $155.94   11.424%   $173.7546   $173.75   $173.75   $173.80  
  Purchase #2 $122.75   12.140%   $137.6519   $137.65   $137.65   $137.70  
  Purchase #3 $59.27   13.473%   $67.2554   $67.26   $67.25   $67.30  
  Purchase #4 $117.44   10.662%   $129.9615   $129.96   $129.95   $130.00  
  Purchase #5 $44.65   7.495%   $47.9965   $48.00   $48.00   $48.00  
  Purchase #6 $125.72   12.301%   $141.1848   $141.18   $141.20   $141.20  
  Purchase #7 $240.64   6.289%   $255.7738   $255.77   $255.75   $255.80  
  7 purchase totals = $866.41       $953.5785   $953.57   $953.55   $953.80