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 $64.33   6.852%   $68.7379   $68.74   $68.75   $68.70  
  Purchase #2 $167.35   13.305%   $189.6159   $189.62   $189.60   $189.60  
  Purchase #3 $121.99   12.110%   $136.763   $136.76   $136.75   $136.80  
  Purchase #4 $66.67   3.153%   $68.7721   $68.77   $68.75   $68.80  
  Purchase #5 $158.87   5.234%   $167.1853   $167.19   $167.20   $167.20  
  Purchase #6 $164.62   3.831%   $170.9266   $170.93   $170.95   $170.90  
  Purchase #7 $133.65   9.447%   $146.2759   $146.28   $146.30   $146.30  
  7 purchase totals = $877.48       $948.2767   $948.29   $948.30   $948.30