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 $142.95   7.206%   $153.251   $153.25   $153.25   $153.30  
  Purchase #2 $203.95   7.858%   $219.9764   $219.98   $220.00   $220.00  
  Purchase #3 $30.72   12.182%   $34.4623   $34.46   $34.45   $34.50  
  Purchase #4 $217.59   3.186%   $224.5224   $224.52   $224.50   $224.50  
  Purchase #5 $44.91   6.259%   $47.7209   $47.72   $47.70   $47.70  
  Purchase #6 $91.26   6.422%   $97.1207   $97.12   $97.10   $97.10  
  Purchase #7 $184.34   12.772%   $207.8839   $207.88   $207.90   $207.90  
  7 purchase totals = $915.72       $984.9376   $984.93   $984.90   $985.00