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	$229.71	7.794%	$247.6136	$247.61	$247.60	$247.60
Purchase #2	$151.57	13.362%	$171.8228	$171.82	$171.80	$171.80
Purchase #3	$207.60	7.151%	$222.4455	$222.45	$222.45	$222.40
Purchase #4	$29.58	11.104%	$32.8646	$32.86	$32.85	$32.90
Purchase #5	$101.87	11.353%	$113.4353	$113.44	$113.45	$113.40
Purchase #6	$127.62	10.317%	$140.7866	$140.79	$140.80	$140.80
Purchase #7	$222.34	6.559%	$236.9233	$236.92	$236.90	$236.90
7 purchase totals =	$1,070.29		$1,165.8917	$1,165.89	$1,165.85	$1,165.80