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 $61.71   3.826%   $64.071   $64.07   $64.05   $64.10  
  Purchase #2 $128.70   4.832%   $134.9188   $134.92   $134.90   $134.90  
  Purchase #3 $86.89   6.229%   $92.3024   $92.30   $92.30   $92.30  
  Purchase #4 $153.80   7.373%   $165.1397   $165.14   $165.15   $165.10  
  Purchase #5 $23.96   8.345%   $25.9595   $25.96   $25.95   $26.00  
  Purchase #6 $235.97   10.611%   $261.0088   $261.01   $261.00   $261.00  
  Purchase #7 $199.70   5.145%   $209.9746   $209.97   $209.95   $210.00  
  7 purchase totals = $890.73       $953.3748   $953.37   $953.30   $953.40