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	$145.45	3.234%	$150.1539	$150.15	$150.15	$150.20
Purchase #2	$148.44	3.706%	$153.9412	$153.94	$153.95	$153.90
Purchase #3	$64.55	13.716%	$73.4037	$73.40	$73.40	$73.40
Purchase #4	$33.41	12.478%	$37.5789	$37.58	$37.60	$37.60
Purchase #5	$99.58	13.207%	$112.7315	$112.73	$112.75	$112.70
Purchase #6	$38.67	6.329%	$41.1174	$41.12	$41.10	$41.10
Purchase #7	$53.90	12.406%	$60.5868	$60.59	$60.60	$60.60
7 purchase totals =	$584.00		$629.5134	$629.51	$629.55	$629.50