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 $40.90   10.828%   $45.3287   $45.33   $45.35   $45.30  
  Purchase #2 $171.58   10.823%   $190.1501   $190.15   $190.15   $190.20  
  Purchase #3 $54.79   4.664%   $57.3454   $57.35   $57.35   $57.30  
  Purchase #4 $106.29   11.391%   $118.3975   $118.40   $118.40   $118.40  
  Purchase #5 $79.25   4.185%   $82.5666   $82.57   $82.55   $82.60  
  Purchase #6 $171.27   5.320%   $180.3816   $180.38   $180.40   $180.40  
  Purchase #7 $86.97   11.218%   $96.7263   $96.73   $96.75   $96.70  
  7 purchase totals = $711.05       $770.8962   $770.91   $770.95   $770.90