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 $177.42   13.583%   $201.519   $201.52   $201.50   $201.50  
  Purchase #2 $40.75   7.409%   $43.7692   $43.77   $43.75   $43.80  
  Purchase #3 $105.96   6.785%   $113.1494   $113.15   $113.15   $113.10  
  Purchase #4 $31.65   5.169%   $33.286   $33.29   $33.30   $33.30  
  Purchase #5 $95.80   4.420%   $100.0344   $100.03   $100.05   $100.00  
  Purchase #6 $229.35   3.151%   $236.5768   $236.58   $236.60   $236.60  
  Purchase #7 $66.59   12.590%   $74.9737   $74.97   $74.95   $75.00  
  7 purchase totals = $747.52       $803.3085   $803.31   $803.30   $803.30