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 $185.65   11.674%   $207.3228   $207.32   $207.30   $207.30  
  Purchase #2 $233.38   12.123%   $261.6727   $261.67   $261.65   $261.70  
  Purchase #3 $122.53   11.124%   $136.1602   $136.16   $136.15   $136.20  
  Purchase #4 $195.26   11.416%   $217.5509   $217.55   $217.55   $217.60  
  Purchase #5 $89.81   4.196%   $93.5784   $93.58   $93.60   $93.60  
  Purchase #6 $193.74   6.309%   $205.9631   $205.96   $205.95   $206.00  
  Purchase #7 $187.68   8.342%   $203.3363   $203.34   $203.35   $203.30  
  7 purchase totals = $1,208.05       $1,325.5844   $1,325.58   $1,325.55   $1,325.70