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 $38.77   12.451%   $43.5973   $43.60   $43.60   $43.60  
  Purchase #2 $182.77   12.795%   $206.1554   $206.16   $206.15   $206.20  
  Purchase #3 $221.52   4.575%   $231.6545   $231.65   $231.65   $231.70  
  Purchase #4 $59.98   10.372%   $66.2011   $66.20   $66.20   $66.20  
  Purchase #5 $199.90   6.797%   $213.4872   $213.49   $213.50   $213.50  
  Purchase #6 $92.49   5.275%   $97.3688   $97.37   $97.35   $97.40  
  Purchase #7 $169.29   9.207%   $184.8765   $184.88   $184.90   $184.90  
  7 purchase totals = $964.72       $1,043.3408   $1,043.35   $1,043.35   $1,043.50