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 $87.64   12.327%   $98.4434   $98.44   $98.45   $98.40  
  Purchase #2 $245.52   6.839%   $262.3111   $262.31   $262.30   $262.30  
  Purchase #3 $129.37   3.457%   $133.8423   $133.84   $133.85   $133.80  
  Purchase #4 $231.47   8.454%   $251.0385   $251.04   $251.05   $251.00  
  Purchase #5 $199.92   4.679%   $209.2743   $209.27   $209.25   $209.30  
  Purchase #6 $156.34   6.226%   $166.0737   $166.07   $166.05   $166.10  
  Purchase #7 $195.54   6.118%   $207.5031   $207.50   $207.50   $207.50  
  7 purchase totals = $1,245.80       $1,328.4864   $1,328.47   $1,328.45   $1,328.40