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 $93.46   10.348%   $103.1312   $103.13   $103.15   $103.10  
  Purchase #2 $66.82   9.780%   $73.355   $73.36   $73.35   $73.40  
  Purchase #3 $127.86   10.411%   $141.1715   $141.17   $141.15   $141.20  
  Purchase #4 $73.28   11.441%   $81.664   $81.66   $81.65   $81.70  
  Purchase #5 $47.98   9.511%   $52.5434   $52.54   $52.55   $52.50  
  Purchase #6 $218.33   8.198%   $236.2287   $236.23   $236.25   $236.20  
  Purchase #7 $34.53   5.241%   $36.3397   $36.34   $36.35   $36.30  
  7 purchase totals = $662.26       $724.4335   $724.43   $724.45   $724.40