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 $208.31   11.862%   $233.0197   $233.02   $233.00   $233.00  
  Purchase #2 $99.78   9.198%   $108.9578   $108.96   $108.95   $109.00  
  Purchase #3 $97.87   9.302%   $106.9739   $106.97   $106.95   $107.00  
  Purchase #4 $110.96   7.249%   $119.0035   $119.00   $119.00   $119.00  
  Purchase #5 $64.67   13.815%   $73.6042   $73.60   $73.60   $73.60  
  Purchase #6 $69.54   11.513%   $77.5461   $77.55   $77.55   $77.50  
  Purchase #7 $74.49   10.377%   $82.2198   $82.22   $82.20   $82.20  
  7 purchase totals = $725.62       $801.3250   $801.32   $801.25   $801.30