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 $156.35   10.782%   $173.2077   $173.21   $173.20   $173.20  
  Purchase #2 $197.78   4.244%   $206.1738   $206.17   $206.15   $206.20  
  Purchase #3 $183.68   9.588%   $201.2912   $201.29   $201.30   $201.30  
  Purchase #4 $125.53   11.412%   $139.8555   $139.86   $139.85   $139.90  
  Purchase #5 $47.78   13.672%   $54.3125   $54.31   $54.30   $54.30  
  Purchase #6 $23.97   6.178%   $25.4509   $25.45   $25.45   $25.50  
  Purchase #7 $189.52   3.416%   $195.994   $195.99   $196.00   $196.00  
  7 purchase totals = $924.61       $996.2856   $996.28   $996.25   $996.40