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 $219.86   9.811%   $241.4305   $241.43   $241.45   $241.40  
  Purchase #2 $112.62   6.109%   $119.5   $119.50   $119.50   $119.50  
  Purchase #3 $18.87   8.405%   $20.456   $20.46   $20.45   $20.50  
  Purchase #4 $220.59   7.737%   $237.657   $237.66   $237.65   $237.70  
  Purchase #5 $178.85   9.269%   $195.4276   $195.43   $195.45   $195.40  
  Purchase #6 $237.43   5.639%   $250.8187   $250.82   $250.80   $250.80  
  Purchase #7 $205.37   5.743%   $217.1644   $217.16   $217.15   $217.20  
  7 purchase totals = $1,193.59       $1,282.4542   $1,282.46   $1,282.45   $1,282.50