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	$85.41	5.534%	$90.1366	$90.14	$90.15	$90.10
Purchase #2	$56.87	13.211%	$64.3831	$64.38	$64.40	$64.40
Purchase #3	$17.48	12.566%	$19.6765	$19.68	$19.70	$19.70
Purchase #4	$159.59	8.340%	$172.8998	$172.90	$172.90	$172.90
Purchase #5	$30.71	7.199%	$32.9208	$32.92	$32.90	$32.90
Purchase #6	$71.64	3.498%	$74.146	$74.15	$74.15	$74.10
Purchase #7	$247.47	11.462%	$275.835	$275.84	$275.85	$275.80
7 purchase totals =	$669.17		$729.9978	$730.01	$730.05	$729.90