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 $103.84   11.841%   $116.1357   $116.14   $116.15   $116.10  
  Purchase #2 $53.61   6.823%   $57.2678   $57.27   $57.25   $57.30  
  Purchase #3 $233.67   3.212%   $241.1755   $241.18   $241.20   $241.20  
  Purchase #4 $146.73   9.828%   $161.1506   $161.15   $161.15   $161.20  
  Purchase #5 $120.73   10.719%   $133.671   $133.67   $133.65   $133.70  
  Purchase #6 $58.25   11.315%   $64.841   $64.84   $64.85   $64.80  
  Purchase #7 $244.82   8.838%   $266.4572   $266.46   $266.45   $266.50  
  7 purchase totals = $961.65       $1,040.6988   $1,040.71   $1,040.70   $1,040.80