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	$148.42	11.271%	$165.1484	$165.15	$165.15	$165.10
Purchase #2	$166.94	3.501%	$172.7846	$172.78	$172.80	$172.80
Purchase #3	$132.35	7.212%	$141.8951	$141.90	$141.90	$141.90
Purchase #4	$208.51	3.776%	$216.3833	$216.38	$216.40	$216.40
Purchase #5	$44.77	12.323%	$50.287	$50.29	$50.30	$50.30
Purchase #6	$176.94	10.423%	$195.3825	$195.38	$195.40	$195.40
Purchase #7	$189.29	5.804%	$200.2764	$200.28	$200.30	$200.30
7 purchase totals =	$1,067.22		$1,142.1573	$1,142.16	$1,142.25	$1,142.20