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 $135.41   6.806%   $144.626   $144.63   $144.65   $144.60  
  Purchase #2 $30.42   7.473%   $32.6933   $32.69   $32.70   $32.70  
  Purchase #3 $53.57   4.456%   $55.9571   $55.96   $55.95   $56.00  
  Purchase #4 $93.79   3.146%   $96.7406   $96.74   $96.75   $96.70  
  Purchase #5 $217.82   7.438%   $234.0215   $234.02   $234.00   $234.00  
  Purchase #6 $226.89   8.546%   $246.28   $246.28   $246.30   $246.30  
  Purchase #7 $72.86   12.801%   $82.1868   $82.19   $82.20   $82.20  
  7 purchase totals = $830.76       $892.5053   $892.51   $892.55   $892.50