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 $151.84   9.649%   $166.491   $166.49   $166.50   $166.50  
  Purchase #2 $192.97   4.757%   $202.1496   $202.15   $202.15   $202.10  
  Purchase #3 $124.86   10.283%   $137.6994   $137.70   $137.70   $137.70  
  Purchase #4 $25.62   4.828%   $26.8569   $26.86   $26.85   $26.90  
  Purchase #5 $193.55   9.412%   $211.7669   $211.77   $211.75   $211.80  
  Purchase #6 $149.55   13.233%   $169.34   $169.34   $169.35   $169.30  
  Purchase #7 $250.43   12.179%   $280.9299   $280.93   $280.95   $280.90  
  7 purchase totals = $1,088.82       $1,195.2337   $1,195.24   $1,195.25   $1,195.20