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 $6.29   7.660%   $6.7718   $6.77   $6.75   $6.80  
  Purchase #2 $233.81   3.397%   $241.7525   $241.75   $241.75   $241.80  
  Purchase #3 $242.25   8.553%   $262.9696   $262.97   $262.95   $263.00  
  Purchase #4 $131.77   10.761%   $145.9498   $145.95   $145.95   $145.90  
  Purchase #5 $14.25   9.300%   $15.5753   $15.58   $15.60   $15.60  
  Purchase #6 $226.50   13.232%   $256.4705   $256.47   $256.45   $256.50  
  Purchase #7 $97.59   4.161%   $101.6507   $101.65   $101.65   $101.70  
  7 purchase totals = $952.46       $1,031.1402   $1,031.14   $1,031.10   $1,031.30