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 $164.43   8.761%   $178.8357   $178.84   $178.85   $178.80  
  Purchase #2 $205.76   13.405%   $233.3421   $233.34   $233.35   $233.30  
  Purchase #3 $160.59   5.693%   $169.7324   $169.73   $169.75   $169.70  
  Purchase #4 $174.39   4.863%   $182.8706   $182.87   $182.85   $182.90  
  Purchase #5 $148.35   6.136%   $157.4528   $157.45   $157.45   $157.50  
  Purchase #6 $23.50   12.482%   $26.4333   $26.43   $26.45   $26.40  
  Purchase #7 $79.70   4.456%   $83.2514   $83.25   $83.25   $83.30  
  7 purchase totals = $956.72       $1,031.9183   $1,031.91   $1,031.95   $1,031.90