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 $95.56   12.345%   $107.3569   $107.36   $107.35   $107.40  
  Purchase #2 $174.66   12.378%   $196.2794   $196.28   $196.30   $196.30  
  Purchase #3 $233.29   4.829%   $244.5556   $244.56   $244.55   $244.60  
  Purchase #4 $47.63   8.252%   $51.5604   $51.56   $51.55   $51.60  
  Purchase #5 $230.32   8.235%   $249.2869   $249.29   $249.30   $249.30  
  Purchase #6 $184.76   3.465%   $191.1619   $191.16   $191.15   $191.20  
  Purchase #7 $22.46   11.775%   $25.1047   $25.10   $25.10   $25.10  
  7 purchase totals = $988.68       $1,065.3058   $1,065.31   $1,065.30   $1,065.50