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 $177.60   13.213%   $201.0663   $201.07   $201.05   $201.10  
  Purchase #2 $112.29   6.372%   $119.4451   $119.45   $119.45   $119.40  
  Purchase #3 $71.95   3.303%   $74.3265   $74.33   $74.35   $74.30  
  Purchase #4 $245.39   9.307%   $268.2284   $268.23   $268.25   $268.20  
  Purchase #5 $246.81   13.281%   $279.5888   $279.59   $279.60   $279.60  
  Purchase #6 $46.55   11.703%   $51.9977   $52.00   $52.00   $52.00  
  Purchase #7 $173.29   5.382%   $182.6165   $182.62   $182.60   $182.60  
  7 purchase totals = $1,073.88       $1,177.2693   $1,177.29   $1,177.30   $1,177.20