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 $159.46   6.468%   $169.7739   $169.77   $169.75   $169.80  
  Purchase #2 $111.33   6.175%   $118.2046   $118.20   $118.20   $118.20  
  Purchase #3 $215.37   4.440%   $224.9324   $224.93   $224.95   $224.90  
  Purchase #4 $23.40   13.492%   $26.5571   $26.56   $26.55   $26.60  
  Purchase #5 $167.92   10.604%   $185.7262   $185.73   $185.75   $185.70  
  Purchase #6 $43.32   11.838%   $48.4482   $48.45   $48.45   $48.40  
  Purchase #7 $161.58   5.754%   $170.8773   $170.88   $170.90   $170.90  
  7 purchase totals = $882.38       $944.5197   $944.52   $944.55   $944.50