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	$92.46	7.640%	$99.5239	$99.52	$99.50	$99.50
Purchase #2	$191.54	12.306%	$215.1109	$215.11	$215.10	$215.10
Purchase #3	$221.90	6.151%	$235.5491	$235.55	$235.55	$235.50
Purchase #4	$122.42	4.849%	$128.3561	$128.36	$128.35	$128.40
Purchase #5	$154.56	7.677%	$166.4256	$166.43	$166.45	$166.40
Purchase #6	$105.62	13.748%	$120.1406	$120.14	$120.15	$120.10
Purchase #7	$146.32	4.235%	$152.5167	$152.52	$152.50	$152.50
7 purchase totals =	$1,034.82		$1,117.6229	$1,117.63	$1,117.60	$1,117.50