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 $204.74   13.860%   $233.117   $233.12   $233.10   $233.10  
  Purchase #2 $119.41   5.241%   $125.6683   $125.67   $125.65   $125.70  
  Purchase #3 $16.28   8.800%   $17.7126   $17.71   $17.70   $17.70  
  Purchase #4 $81.43   11.385%   $90.7008   $90.70   $90.70   $90.70  
  Purchase #5 $146.76   9.620%   $160.8783   $160.88   $160.90   $160.90  
  Purchase #6 $221.27   9.669%   $242.6646   $242.66   $242.65   $242.70  
  Purchase #7 $141.62   7.267%   $151.9115   $151.91   $151.90   $151.90  
  7 purchase totals = $931.51       $1,022.6531   $1,022.65   $1,022.60   $1,022.70