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	$239.53	10.338%	$264.2926	$264.29	$264.30	$264.30
Purchase #2	$162.44	6.212%	$172.5308	$172.53	$172.55	$172.50
Purchase #3	$70.54	5.849%	$74.6659	$74.67	$74.65	$74.70
Purchase #4	$161.57	3.560%	$167.3219	$167.32	$167.30	$167.30
Purchase #5	$78.66	12.386%	$88.4028	$88.40	$88.40	$88.40
Purchase #6	$57.68	7.150%	$61.8041	$61.80	$61.80	$61.80
Purchase #7	$140.86	5.388%	$148.4495	$148.45	$148.45	$148.40
7 purchase totals =	$911.28		$977.4676	$977.46	$977.45	$977.40