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	$61.71	4.651%	$64.5801	$64.58	$64.60	$64.60
Purchase #2	$243.44	13.196%	$275.5643	$275.56	$275.55	$275.60
Purchase #3	$97.70	8.532%	$106.0358	$106.04	$106.05	$106.00
Purchase #4	$22.92	12.856%	$25.8666	$25.87	$25.85	$25.90
Purchase #5	$37.74	12.583%	$42.4888	$42.49	$42.50	$42.50
Purchase #6	$59.71	13.431%	$67.7297	$67.73	$67.75	$67.70
Purchase #7	$154.63	4.835%	$162.1064	$162.11	$162.10	$162.10
7 purchase totals =	$677.85		$744.3717	$744.38	$744.40	$744.40