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 $107.59   11.151%   $119.5874   $119.59   $119.60   $119.60  
  Purchase #2 $165.98   13.667%   $188.6645   $188.66   $188.65   $188.70  
  Purchase #3 $162.44   10.159%   $178.9423   $178.94   $178.95   $178.90  
  Purchase #4 $125.41   8.663%   $136.2743   $136.27   $136.25   $136.30  
  Purchase #5 $96.99   13.790%   $110.3649   $110.36   $110.35   $110.40  
  Purchase #6 $100.55   11.413%   $112.0258   $112.03   $112.05   $112.00  
  Purchase #7 $22.55   4.181%   $23.4928   $23.49   $23.50   $23.50  
  7 purchase totals = $781.51       $869.3520   $869.34   $869.35   $869.40