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 $240.73   11.605%   $268.6667   $268.67   $268.65   $268.70  
  Purchase #2 $148.54   7.651%   $159.9048   $159.90   $159.90   $159.90  
  Purchase #3 $5.58   3.631%   $5.7826   $5.78   $5.80   $5.80  
  Purchase #4 $46.91   3.662%   $48.6278   $48.63   $48.65   $48.60  
  Purchase #5 $71.85   11.469%   $80.0905   $80.09   $80.10   $80.10  
  Purchase #6 $192.92   11.868%   $215.8157   $215.82   $215.80   $215.80  
  Purchase #7 $112.51   3.162%   $116.0676   $116.07   $116.05   $116.10  
  7 purchase totals = $819.04       $894.9557   $894.96   $894.95   $895.00