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	$90.56	11.840%	$101.2823	$101.28	$101.30	$101.30
Purchase #2	$130.37	12.400%	$146.5359	$146.54	$146.55	$146.50
Purchase #3	$61.44	6.753%	$65.589	$65.59	$65.60	$65.60
Purchase #4	$203.93	7.643%	$219.5164	$219.52	$219.50	$219.50
Purchase #5	$51.72	3.162%	$53.3554	$53.36	$53.35	$53.40
Purchase #6	$17.67	5.425%	$18.6286	$18.63	$18.65	$18.60
Purchase #7	$111.27	8.313%	$120.5199	$120.52	$120.50	$120.50
7 purchase totals =	$666.96		$725.4275	$725.44	$725.45	$725.40