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 $61.91   3.381%   $64.0032   $64.00   $64.00   $64.00  
  Purchase #2 $101.63   8.499%   $110.2675   $110.27   $110.25   $110.30  
  Purchase #3 $107.50   9.267%   $117.462   $117.46   $117.45   $117.50  
  Purchase #4 $189.54   13.654%   $215.4198   $215.42   $215.40   $215.40  
  Purchase #5 $243.86   6.633%   $260.0352   $260.04   $260.05   $260.00  
  Purchase #6 $86.90   12.803%   $98.0258   $98.03   $98.05   $98.00  
  Purchase #7 $167.39   9.316%   $182.9841   $182.98   $183.00   $183.00  
  7 purchase totals = $958.73       $1,048.1976   $1,048.20   $1,048.20   $1,048.20