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 $84.37   9.795%   $92.634   $92.63   $92.65   $92.60  
  Purchase #2 $146.50   4.594%   $153.2302   $153.23   $153.25   $153.20  
  Purchase #3 $11.25   8.229%   $12.1758   $12.18   $12.20   $12.20  
  Purchase #4 $225.53   13.858%   $256.7839   $256.78   $256.80   $256.80  
  Purchase #5 $33.76   8.389%   $36.5921   $36.59   $36.60   $36.60  
  Purchase #6 $177.44   3.133%   $182.9992   $183.00   $183.00   $183.00  
  Purchase #7 $78.96   9.308%   $86.3096   $86.31   $86.30   $86.30  
  7 purchase totals = $757.81       $820.7248   $820.72   $820.80   $820.70