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 $243.41   9.475%   $266.4731   $266.47   $266.45   $266.50  
  Purchase #2 $201.27   13.563%   $228.5683   $228.57   $228.55   $228.60  
  Purchase #3 $82.29   4.863%   $86.2918   $86.29   $86.30   $86.30  
  Purchase #4 $169.69   10.818%   $188.0471   $188.05   $188.05   $188.00  
  Purchase #5 $71.71   3.228%   $74.0248   $74.02   $74.00   $74.00  
  Purchase #6 $118.81   11.841%   $132.8783   $132.88   $132.90   $132.90  
  Purchase #7 $46.79   5.447%   $49.3387   $49.34   $49.35   $49.30  
  7 purchase totals = $933.97       $1,025.6221   $1,025.62   $1,025.60   $1,025.60