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 $233.65   10.543%   $258.2837   $258.28   $258.30   $258.30  
  Purchase #2 $188.56   3.604%   $195.3557   $195.36   $195.35   $195.40  
  Purchase #3 $177.29   3.162%   $182.8959   $182.90   $182.90   $182.90  
  Purchase #4 $201.68   9.511%   $220.8618   $220.86   $220.85   $220.90  
  Purchase #5 $201.84   13.817%   $229.7282   $229.73   $229.75   $229.70  
  Purchase #6 $24.37   6.255%   $25.8943   $25.89   $25.90   $25.90  
  Purchase #7 $227.47   11.870%   $254.4707   $254.47   $254.45   $254.50  
  7 purchase totals = $1,254.86       $1,367.4903   $1,367.49   $1,367.50   $1,367.60