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 $113.65   8.353%   $123.1432   $123.14   $123.15   $123.10  
  Purchase #2 $84.67   12.149%   $94.9566   $94.96   $94.95   $95.00  
  Purchase #3 $108.34   6.756%   $115.6595   $115.66   $115.65   $115.70  
  Purchase #4 $156.47   8.307%   $169.468   $169.47   $169.45   $169.50  
  Purchase #5 $18.54   12.377%   $20.8347   $20.83   $20.85   $20.80  
  Purchase #6 $97.29   8.566%   $105.6239   $105.62   $105.60   $105.60  
  Purchase #7 $249.96   3.117%   $257.7513   $257.75   $257.75   $257.80  
  7 purchase totals = $828.92       $887.4372   $887.43   $887.40   $887.50