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 $94.49   7.743%   $101.8064   $101.81   $101.80   $101.80  
  Purchase #2 $119.84   12.118%   $134.3622   $134.36   $134.35   $134.40  
  Purchase #3 $53.73   9.355%   $58.7564   $58.76   $58.75   $58.80  
  Purchase #4 $197.46   4.296%   $205.9429   $205.94   $205.95   $205.90  
  Purchase #5 $98.47   7.547%   $105.9015   $105.90   $105.90   $105.90  
  Purchase #6 $200.83   4.525%   $209.9176   $209.92   $209.90   $209.90  
  Purchase #7 $112.93   11.516%   $125.935   $125.94   $125.95   $125.90  
  7 purchase totals = $877.75       $942.6220   $942.63   $942.60   $942.60