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 $232.68   11.152%   $258.6285   $258.63   $258.65   $258.60  
  Purchase #2 $178.28   4.522%   $186.3418   $186.34   $186.35   $186.30  
  Purchase #3 $40.52   11.535%   $45.194   $45.19   $45.20   $45.20  
  Purchase #4 $190.88   6.203%   $202.7203   $202.72   $202.70   $202.70  
  Purchase #5 $37.84   6.206%   $40.1884   $40.19   $40.20   $40.20  
  Purchase #6 $73.33   13.854%   $83.4891   $83.49   $83.50   $83.50  
  Purchase #7 $215.39   6.754%   $229.9374   $229.94   $229.95   $229.90  
  7 purchase totals = $968.92       $1,046.4995   $1,046.50   $1,046.55   $1,046.40