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	$199.39	5.586%	$210.5279	$210.53	$210.55	$210.50
Purchase #2	$173.52	12.618%	$195.4148	$195.41	$195.40	$195.40
Purchase #3	$234.77	9.228%	$256.4346	$256.43	$256.45	$256.40
Purchase #4	$88.55	12.355%	$99.4904	$99.49	$99.50	$99.50
Purchase #5	$214.73	8.672%	$233.3514	$233.35	$233.35	$233.40
Purchase #6	$145.32	11.764%	$162.4154	$162.42	$162.40	$162.40
Purchase #7	$111.79	6.257%	$118.7847	$118.78	$118.80	$118.80
7 purchase totals =	$1,168.07		$1,276.4192	$1,276.41	$1,276.45	$1,276.40