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 $89.73   5.437%   $94.6086   $94.61   $94.60   $94.60  
  Purchase #2 $213.29   5.219%   $224.4216   $224.42   $224.40   $224.40  
  Purchase #3 $61.58   12.325%   $69.1697   $69.17   $69.15   $69.20  
  Purchase #4 $169.40   12.858%   $191.1815   $191.18   $191.20   $191.20  
  Purchase #5 $133.63   11.790%   $149.385   $149.39   $149.40   $149.40  
  Purchase #6 $67.79   6.108%   $71.9306   $71.93   $71.95   $71.90  
  Purchase #7 $81.53   13.566%   $92.5904   $92.59   $92.60   $92.60  
  7 purchase totals = $816.95       $893.2874   $893.29   $893.30   $893.30