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 $42.66   13.845%   $48.5663   $48.57   $48.55   $48.60  
  Purchase #2 $216.70   12.431%   $243.638   $243.64   $243.65   $243.60  
  Purchase #3 $15.82   11.193%   $17.5907   $17.59   $17.60   $17.60  
  Purchase #4 $161.40   4.624%   $168.8631   $168.86   $168.85   $168.90  
  Purchase #5 $55.84   7.848%   $60.2223   $60.22   $60.20   $60.20  
  Purchase #6 $56.84   6.677%   $60.6352   $60.64   $60.65   $60.60  
  Purchase #7 $200.92   7.233%   $215.4525   $215.45   $215.45   $215.50  
  7 purchase totals = $750.18       $814.9681   $814.97   $814.95   $815.00