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 $241.93   8.606%   $262.7505   $262.75   $262.75   $262.80  
  Purchase #2 $223.54   4.731%   $234.1157   $234.12   $234.10   $234.10  
  Purchase #3 $21.48   11.282%   $23.9034   $23.90   $23.90   $23.90  
  Purchase #4 $82.45   10.253%   $90.9036   $90.90   $90.90   $90.90  
  Purchase #5 $79.56   9.561%   $87.1667   $87.17   $87.15   $87.20  
  Purchase #6 $125.97   5.547%   $132.9576   $132.96   $132.95   $133.00  
  Purchase #7 $63.83   5.680%   $67.4555   $67.46   $67.45   $67.50  
  7 purchase totals = $838.76       $899.2530   $899.26   $899.20   $899.40