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 $82.43   12.775%   $92.9604   $92.96   $92.95   $93.00  
  Purchase #2 $231.61   10.676%   $256.3367   $256.34   $256.35   $256.30  
  Purchase #3 $167.61   12.754%   $188.987   $188.99   $189.00   $189.00  
  Purchase #4 $80.43   8.330%   $87.1298   $87.13   $87.15   $87.10  
  Purchase #5 $65.84   6.211%   $69.9293   $69.93   $69.95   $69.90  
  Purchase #6 $97.75   3.177%   $100.8555   $100.86   $100.85   $100.90  
  Purchase #7 $156.57   8.874%   $170.464   $170.46   $170.45   $170.50  
  7 purchase totals = $882.24       $966.6627   $966.67   $966.70   $966.70