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 $241.32   9.630%   $264.5591   $264.56   $264.55   $264.60  
  Purchase #2 $212.71   6.453%   $226.4362   $226.44   $226.45   $226.40  
  Purchase #3 $117.83   9.811%   $129.3903   $129.39   $129.40   $129.40  
  Purchase #4 $242.79   4.336%   $253.3174   $253.32   $253.30   $253.30  
  Purchase #5 $143.68   5.712%   $151.887   $151.89   $151.90   $151.90  
  Purchase #6 $173.48   3.678%   $179.8606   $179.86   $179.85   $179.90  
  Purchase #7 $227.62   8.291%   $246.492   $246.49   $246.50   $246.50  
  7 purchase totals = $1,359.43       $1,451.9426   $1,451.95   $1,451.95   $1,452.00