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	$51.26	12.205%	$57.5163	$57.52	$57.50	$57.50
Purchase #2	$118.98	7.172%	$127.5132	$127.51	$127.50	$127.50
Purchase #3	$52.68	12.636%	$59.3366	$59.34	$59.35	$59.30
Purchase #4	$78.75	12.437%	$88.5441	$88.54	$88.55	$88.50
Purchase #5	$9.57	12.194%	$10.737	$10.74	$10.75	$10.70
Purchase #6	$86.98	4.361%	$90.7732	$90.77	$90.75	$90.80
Purchase #7	$35.64	10.717%	$39.4595	$39.46	$39.45	$39.50
7 purchase totals =	$433.86		$473.8799	$473.88	$473.85	$473.80