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	$234.73	3.472%	$242.8798	$242.88	$242.90	$242.90
Purchase #2	$142.29	13.559%	$161.5831	$161.58	$161.60	$161.60
Purchase #3	$112.72	4.741%	$118.0641	$118.06	$118.05	$118.10
Purchase #4	$191.82	13.161%	$217.0654	$217.07	$217.05	$217.10
Purchase #5	$32.35	4.242%	$33.7223	$33.72	$33.70	$33.70
Purchase #6	$250.38	5.806%	$264.9171	$264.92	$264.90	$264.90
Purchase #7	$48.31	8.537%	$52.4342	$52.43	$52.45	$52.40
7 purchase totals =	$1,012.60		$1,090.6660	$1,090.66	$1,090.65	$1,090.70