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 $227.64   3.231%   $234.995   $235.00   $235.00   $235.00  
  Purchase #2 $101.96   5.769%   $107.8421   $107.84   $107.85   $107.80  
  Purchase #3 $22.71   3.538%   $23.5135   $23.51   $23.50   $23.50  
  Purchase #4 $125.63   5.850%   $132.9794   $132.98   $133.00   $133.00  
  Purchase #5 $222.38   10.653%   $246.0701   $246.07   $246.05   $246.10  
  Purchase #6 $68.71   3.377%   $71.0303   $71.03   $71.05   $71.00  
  Purchase #7 $10.73   4.374%   $11.1993   $11.20   $11.20   $11.20  
  7 purchase totals = $779.76       $827.6297   $827.63   $827.65   $827.60