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 $218.35   13.401%   $247.6111   $247.61   $247.60   $247.60  
  Purchase #2 $56.83   13.303%   $64.3901   $64.39   $64.40   $64.40  
  Purchase #3 $109.72   8.427%   $118.9661   $118.97   $118.95   $119.00  
  Purchase #4 $247.63   10.339%   $273.2325   $273.23   $273.25   $273.20  
  Purchase #5 $25.51   9.722%   $27.9901   $27.99   $28.00   $28.00  
  Purchase #6 $16.36   6.684%   $17.4535   $17.45   $17.45   $17.50  
  Purchase #7 $176.27   13.864%   $200.7081   $200.71   $200.70   $200.70  
  7 purchase totals = $850.67       $950.3515   $950.35   $950.35   $950.40