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 $187.64   10.440%   $207.2296   $207.23   $207.25   $207.20  
  Purchase #2 $249.38   10.346%   $275.1809   $275.18   $275.20   $275.20  
  Purchase #3 $202.49   7.645%   $217.9704   $217.97   $217.95   $218.00  
  Purchase #4 $217.62   7.298%   $233.5019   $233.50   $233.50   $233.50  
  Purchase #5 $179.28   13.713%   $203.8647   $203.86   $203.85   $203.90  
  Purchase #6 $194.29   6.103%   $206.1475   $206.15   $206.15   $206.10  
  Purchase #7 $138.88   11.163%   $154.3832   $154.38   $154.40   $154.40  
  7 purchase totals = $1,369.58       $1,498.2782   $1,498.27   $1,498.30   $1,498.30