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 $62.51   10.709%   $69.2042   $69.20   $69.20   $69.20  
  Purchase #2 $128.93   6.504%   $137.3156   $137.32   $137.30   $137.30  
  Purchase #3 $243.29   5.222%   $255.9946   $255.99   $256.00   $256.00  
  Purchase #4 $206.83   4.431%   $215.9946   $215.99   $216.00   $216.00  
  Purchase #5 $49.54   9.492%   $54.2423   $54.24   $54.25   $54.20  
  Purchase #6 $205.82   10.278%   $226.9742   $226.97   $226.95   $227.00  
  Purchase #7 $183.61   8.218%   $198.6991   $198.70   $198.70   $198.70  
  7 purchase totals = $1,080.53       $1,158.4246   $1,158.41   $1,158.40   $1,158.40