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 $192.72   8.111%   $208.3515   $208.35   $208.35   $208.40  
  Purchase #2 $45.71   7.474%   $49.1264   $49.13   $49.15   $49.10  
  Purchase #3 $105.76   12.582%   $119.0667   $119.07   $119.05   $119.10  
  Purchase #4 $187.92   3.216%   $193.9635   $193.96   $193.95   $194.00  
  Purchase #5 $55.76   3.122%   $57.5008   $57.50   $57.50   $57.50  
  Purchase #6 $191.67   9.102%   $209.1158   $209.12   $209.10   $209.10  
  Purchase #7 $130.43   5.205%   $137.2189   $137.22   $137.20   $137.20  
  7 purchase totals = $909.97       $974.3436   $974.35   $974.30   $974.40