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	$157.57	13.809%	$179.3288	$179.33	$179.35	$179.30
Purchase #2	$85.92	4.483%	$89.7718	$89.77	$89.75	$89.80
Purchase #3	$154.46	8.409%	$167.4485	$167.45	$167.45	$167.40
Purchase #4	$91.98	8.454%	$99.756	$99.76	$99.75	$99.80
Purchase #5	$120.74	5.599%	$127.5002	$127.50	$127.50	$127.50
Purchase #6	$58.60	12.588%	$65.9766	$65.98	$66.00	$66.00
Purchase #7	$217.30	13.578%	$246.805	$246.81	$246.80	$246.80
7 purchase totals =	$886.57		$976.5869	$976.60	$976.60	$976.60