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	$190.79	12.657%	$214.9383	$214.94	$214.95	$214.90
Purchase #2	$123.73	6.390%	$131.6363	$131.64	$131.65	$131.60
Purchase #3	$195.67	13.667%	$222.4122	$222.41	$222.40	$222.40
Purchase #4	$80.99	11.513%	$90.3144	$90.31	$90.30	$90.30
Purchase #5	$41.46	12.529%	$46.6545	$46.65	$46.65	$46.70
Purchase #6	$90.92	10.215%	$100.2075	$100.21	$100.20	$100.20
Purchase #7	$9.91	10.124%	$10.9133	$10.91	$10.90	$10.90
7 purchase totals =	$733.47		$817.0765	$817.07	$817.05	$817.00