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 $202.68   11.324%   $225.6315   $225.63   $225.65   $225.60  
  Purchase #2 $54.67   4.383%   $57.0662   $57.07   $57.05   $57.10  
  Purchase #3 $22.94   7.334%   $24.6224   $24.62   $24.60   $24.60  
  Purchase #4 $49.29   3.290%   $50.9116   $50.91   $50.90   $50.90  
  Purchase #5 $229.94   11.449%   $256.2658   $256.27   $256.25   $256.30  
  Purchase #6 $195.81   9.650%   $214.7057   $214.71   $214.70   $214.70  
  Purchase #7 $211.30   3.417%   $218.5201   $218.52   $218.50   $218.50  
  7 purchase totals = $966.63       $1,047.7233   $1,047.73   $1,047.65   $1,047.70