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	$104.55	13.708%	$118.8817	$118.88	$118.90	$118.90
Purchase #2	$35.35	9.599%	$38.7432	$38.74	$38.75	$38.70
Purchase #3	$156.89	4.579%	$164.074	$164.07	$164.05	$164.10
Purchase #4	$49.31	13.190%	$55.814	$55.81	$55.80	$55.80
Purchase #5	$37.35	10.857%	$41.4051	$41.41	$41.40	$41.40
Purchase #6	$28.46	13.415%	$32.2779	$32.28	$32.30	$32.30
Purchase #7	$185.26	5.489%	$195.4289	$195.43	$195.45	$195.40
7 purchase totals =	$597.17		$646.6248	$646.62	$646.65	$646.60