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	$162.51	6.232%	$172.6376	$172.64	$172.65	$172.60
Purchase #2	$91.71	8.306%	$99.3274	$99.33	$99.35	$99.30
Purchase #3	$108.59	5.181%	$114.216	$114.22	$114.20	$114.20
Purchase #4	$216.76	12.465%	$243.7791	$243.78	$243.80	$243.80
Purchase #5	$40.77	8.579%	$44.2677	$44.27	$44.25	$44.30
Purchase #6	$40.39	13.457%	$45.8253	$45.83	$45.85	$45.80
Purchase #7	$107.75	13.172%	$121.9428	$121.94	$121.95	$121.90
7 purchase totals =	$768.48		$841.9959	$842.01	$842.05	$841.90