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	$93.29	6.308%	$99.1747	$99.17	$99.15	$99.20
Purchase #2	$40.93	6.197%	$43.4664	$43.47	$43.45	$43.50
Purchase #3	$163.79	13.454%	$185.8263	$185.83	$185.85	$185.80
Purchase #4	$101.73	7.788%	$109.6527	$109.65	$109.65	$109.70
Purchase #5	$31.56	5.583%	$33.322	$33.32	$33.30	$33.30
Purchase #6	$54.45	10.729%	$60.2919	$60.29	$60.30	$60.30
Purchase #7	$217.72	9.337%	$238.0485	$238.05	$238.05	$238.00
7 purchase totals =	$703.47		$769.7825	$769.78	$769.75	$769.80