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 $85.28   12.231%   $95.7106   $95.71   $95.70   $95.70  
  Purchase #2 $24.52   9.536%   $26.8582   $26.86   $26.85   $26.90  
  Purchase #3 $85.40   12.831%   $96.3577   $96.36   $96.35   $96.40  
  Purchase #4 $85.77   13.697%   $97.5179   $97.52   $97.50   $97.50  
  Purchase #5 $87.69   5.312%   $92.3481   $92.35   $92.35   $92.30  
  Purchase #6 $155.54   13.752%   $176.9299   $176.93   $176.95   $176.90  
  Purchase #7 $33.29   9.383%   $36.4136   $36.41   $36.40   $36.40  
  7 purchase totals = $557.49       $622.1360   $622.14   $622.10   $622.10