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 $77.33   11.261%   $86.0381   $86.04   $86.05   $86.00  
  Purchase #2 $88.95   5.275%   $93.6421   $93.64   $93.65   $93.60  
  Purchase #3 $53.88   11.355%   $59.9981   $60.00   $60.00   $60.00  
  Purchase #4 $236.33   13.302%   $267.7666   $267.77   $267.75   $267.80  
  Purchase #5 $169.91   7.729%   $183.0423   $183.04   $183.05   $183.00  
  Purchase #6 $91.42   6.659%   $97.5077   $97.51   $97.50   $97.50  
  Purchase #7 $101.27   7.774%   $109.1427   $109.14   $109.15   $109.10  
  7 purchase totals = $819.09       $897.1376   $897.14   $897.15   $897.00