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 $65.42   11.183%   $72.7359   $72.74   $72.75   $72.70  
  Purchase #2 $212.86   7.720%   $229.2928   $229.29   $229.30   $229.30  
  Purchase #3 $59.62   11.353%   $66.3887   $66.39   $66.40   $66.40  
  Purchase #4 $84.33   6.289%   $89.6335   $89.63   $89.65   $89.60  
  Purchase #5 $208.51   13.278%   $236.196   $236.20   $236.20   $236.20  
  Purchase #6 $28.72   12.443%   $32.2936   $32.29   $32.30   $32.30  
  Purchase #7 $208.66   12.664%   $235.0847   $235.08   $235.10   $235.10  
  7 purchase totals = $868.12       $961.6252   $961.62   $961.70   $961.60