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 $96.96   6.558%   $103.3186   $103.32   $103.30   $103.30  
  Purchase #2 $130.90   13.473%   $148.5362   $148.54   $148.55   $148.50  
  Purchase #3 $23.84   7.694%   $25.6742   $25.67   $25.65   $25.70  
  Purchase #4 $15.70   6.141%   $16.6641   $16.66   $16.65   $16.70  
  Purchase #5 $185.36   13.448%   $210.2872   $210.29   $210.30   $210.30  
  Purchase #6 $83.74   11.708%   $93.5443   $93.54   $93.55   $93.50  
  Purchase #7 $189.87   9.868%   $208.6064   $208.61   $208.60   $208.60  
  7 purchase totals = $726.37       $806.6310   $806.63   $806.60   $806.60