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	$34.79	8.238%	$37.656	$37.66	$37.65	$37.70
Purchase #2	$35.55	10.554%	$39.3019	$39.30	$39.30	$39.30
Purchase #3	$93.92	6.870%	$100.3723	$100.37	$100.35	$100.40
Purchase #4	$96.73	13.765%	$110.0449	$110.04	$110.05	$110.00
Purchase #5	$189.85	10.535%	$209.8507	$209.85	$209.85	$209.90
Purchase #6	$153.78	11.166%	$170.9511	$170.95	$170.95	$171.00
Purchase #7	$95.44	5.220%	$100.422	$100.42	$100.40	$100.40
7 purchase totals =	$700.06		$768.5989	$768.59	$768.55	$768.70