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 $88.92   9.651%   $97.5017   $97.50   $97.50   $97.50  
  Purchase #2 $48.86   13.296%   $55.3564   $55.36   $55.35   $55.40  
  Purchase #3 $62.90   3.819%   $65.3022   $65.30   $65.30   $65.30  
  Purchase #4 $108.89   10.140%   $119.9314   $119.93   $119.95   $119.90  
  Purchase #5 $250.34   10.495%   $276.6132   $276.61   $276.60   $276.60  
  Purchase #6 $166.87   4.585%   $174.521   $174.52   $174.50   $174.50  
  Purchase #7 $181.46   7.462%   $195.0005   $195.00   $195.00   $195.00  
  7 purchase totals = $908.24       $984.2264   $984.22   $984.20   $984.20