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	$58.85	13.188%	$66.6111	$66.61	$66.60	$66.60
Purchase #2	$206.94	7.635%	$222.7399	$222.74	$222.75	$222.70
Purchase #3	$218.25	5.494%	$230.2407	$230.24	$230.25	$230.20
Purchase #4	$173.69	8.271%	$188.0559	$188.06	$188.05	$188.10
Purchase #5	$248.53	4.254%	$259.1025	$259.10	$259.10	$259.10
Purchase #6	$162.38	13.554%	$184.389	$184.39	$184.40	$184.40
Purchase #7	$64.46	11.334%	$71.7659	$71.77	$71.75	$71.80
7 purchase totals =	$1,133.10		$1,222.9050	$1,222.91	$1,222.90	$1,222.90