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	$159.34	4.139%	$165.9351	$165.94	$165.95	$165.90
Purchase #2	$46.94	5.368%	$49.4597	$49.46	$49.45	$49.50
Purchase #3	$234.41	5.645%	$247.6424	$247.64	$247.65	$247.60
Purchase #4	$75.56	12.584%	$85.0685	$85.07	$85.05	$85.10
Purchase #5	$171.73	9.162%	$187.4639	$187.46	$187.45	$187.50
Purchase #6	$202.50	11.562%	$225.9131	$225.91	$225.90	$225.90
Purchase #7	$26.89	6.152%	$28.5443	$28.54	$28.55	$28.50
7 purchase totals =	$917.37		$990.0270	$990.02	$990.00	$990.00