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 $49.34   6.203%   $52.4006   $52.40   $52.40   $52.40  
  Purchase #2 $241.71   6.874%   $258.3251   $258.33   $258.35   $258.30  
  Purchase #3 $31.38   6.495%   $33.4181   $33.42   $33.40   $33.40  
  Purchase #4 $236.26   11.457%   $263.3283   $263.33   $263.35   $263.30  
  Purchase #5 $73.80   13.394%   $83.6848   $83.68   $83.70   $83.70  
  Purchase #6 $93.86   8.371%   $101.717   $101.72   $101.70   $101.70  
  Purchase #7 $39.52   3.380%   $40.8558   $40.86   $40.85   $40.90  
  7 purchase totals = $765.87       $833.7297   $833.74   $833.75   $833.70