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 $55.71   13.282%   $63.1094   $63.11   $63.10   $63.10  
  Purchase #2 $133.95   5.392%   $141.1726   $141.17   $141.15   $141.20  
  Purchase #3 $241.96   10.236%   $266.727   $266.73   $266.75   $266.70  
  Purchase #4 $116.80   13.590%   $132.6731   $132.67   $132.65   $132.70  
  Purchase #5 $212.90   9.861%   $233.8941   $233.89   $233.90   $233.90  
  Purchase #6 $167.90   9.267%   $183.4593   $183.46   $183.45   $183.50  
  Purchase #7 $98.57   3.374%   $101.8958   $101.90   $101.90   $101.90  
  7 purchase totals = $1,027.79       $1,122.9313   $1,122.93   $1,122.90   $1,123.00