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 $224.92   13.648%   $255.6171   $255.62   $255.60   $255.60  
  Purchase #2 $166.94   5.689%   $176.4372   $176.44   $176.45   $176.40  
  Purchase #3 $204.49   12.324%   $229.6913   $229.69   $229.70   $229.70  
  Purchase #4 $62.88   8.132%   $67.9934   $67.99   $68.00   $68.00  
  Purchase #5 $22.95   7.624%   $24.6997   $24.70   $24.70   $24.70  
  Purchase #6 $210.50   12.430%   $236.6652   $236.67   $236.65   $236.70  
  Purchase #7 $169.54   13.419%   $192.2906   $192.29   $192.30   $192.30  
  7 purchase totals = $1,062.22       $1,183.3945   $1,183.40   $1,183.40   $1,183.40