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 $22.82   6.498%   $24.3028   $24.30   $24.30   $24.30  
  Purchase #2 $149.85   4.407%   $156.4539   $156.45   $156.45   $156.50  
  Purchase #3 $151.64   8.748%   $164.9055   $164.91   $164.90   $164.90  
  Purchase #4 $193.63   12.342%   $217.5278   $217.53   $217.55   $217.50  
  Purchase #5 $230.93   6.644%   $246.273   $246.27   $246.25   $246.30  
  Purchase #6 $170.32   7.519%   $183.1264   $183.13   $183.15   $183.10  
  Purchase #7 $199.39   8.375%   $216.0889   $216.09   $216.10   $216.10  
  7 purchase totals = $1,118.58       $1,208.6783   $1,208.68   $1,208.70   $1,208.70