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	$11.84	8.414%	$12.8362	$12.84	$12.85	$12.80
Purchase #2	$60.29	8.442%	$65.3797	$65.38	$65.40	$65.40
Purchase #3	$48.65	5.766%	$51.4552	$51.46	$51.45	$51.50
Purchase #4	$234.35	7.265%	$251.3755	$251.38	$251.40	$251.40
Purchase #5	$36.38	11.413%	$40.532	$40.53	$40.55	$40.50
Purchase #6	$29.57	12.176%	$33.1704	$33.17	$33.15	$33.20
Purchase #7	$243.75	12.607%	$274.4796	$274.48	$274.50	$274.50
7 purchase totals =	$664.83		$729.2286	$729.24	$729.30	$729.30