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 $238.77   8.175%   $258.2894   $258.29   $258.30   $258.30  
  Purchase #2 $179.29   4.525%   $187.4029   $187.40   $187.40   $187.40  
  Purchase #3 $16.26   4.528%   $16.9963   $17.00   $17.00   $17.00  
  Purchase #4 $233.68   11.692%   $261.0019   $261.00   $261.00   $261.00  
  Purchase #5 $98.37   5.674%   $103.9515   $103.95   $103.95   $104.00  
  Purchase #6 $42.30   10.723%   $46.8358   $46.84   $46.85   $46.80  
  Purchase #7 $138.80   7.289%   $148.9171   $148.92   $148.90   $148.90  
  7 purchase totals = $947.47       $1,023.3949   $1,023.40   $1,023.40   $1,023.40