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 $55.46   8.306%   $60.0665   $60.07   $60.05   $60.10  
  Purchase #2 $194.53   10.297%   $214.5608   $214.56   $214.55   $214.60  
  Purchase #3 $10.53   11.377%   $11.728   $11.73   $11.75   $11.70  
  Purchase #4 $217.45   7.398%   $233.537   $233.54   $233.55   $233.50  
  Purchase #5 $161.66   8.107%   $174.7658   $174.77   $174.75   $174.80  
  Purchase #6 $48.38   6.361%   $51.4575   $51.46   $51.45   $51.50  
  Purchase #7 $237.32   8.365%   $257.1718   $257.17   $257.15   $257.20  
  7 purchase totals = $925.33       $1,003.2874   $1,003.30   $1,003.25   $1,003.40