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 $223.68   10.222%   $246.5446   $246.54   $246.55   $246.50  
  Purchase #2 $239.78   8.523%   $260.2164   $260.22   $260.20   $260.20  
  Purchase #3 $158.28   3.542%   $163.8863   $163.89   $163.90   $163.90  
  Purchase #4 $143.27   10.457%   $158.2517   $158.25   $158.25   $158.30  
  Purchase #5 $138.70   5.785%   $146.7238   $146.72   $146.70   $146.70  
  Purchase #6 $179.70   4.282%   $187.3948   $187.39   $187.40   $187.40  
  Purchase #7 $152.96   11.146%   $170.0089   $170.01   $170.00   $170.00  
  7 purchase totals = $1,236.37       $1,333.0265   $1,333.02   $1,333.00   $1,333.00