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	$193.89	8.385%	$210.1477	$210.15	$210.15	$210.10
Purchase #2	$39.66	13.593%	$45.051	$45.05	$45.05	$45.10
Purchase #3	$71.32	12.566%	$80.2821	$80.28	$80.30	$80.30
Purchase #4	$26.77	6.166%	$28.4206	$28.42	$28.40	$28.40
Purchase #5	$56.32	3.309%	$58.1836	$58.18	$58.20	$58.20
Purchase #6	$106.45	12.362%	$119.6093	$119.61	$119.60	$119.60
Purchase #7	$94.99	4.826%	$99.5742	$99.57	$99.55	$99.60
7 purchase totals =	$589.40		$641.2685	$641.26	$641.25	$641.30