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	$245.73	12.568%	$276.6133	$276.61	$276.60	$276.60
Purchase #2	$97.51	12.639%	$109.8343	$109.83	$109.85	$109.80
Purchase #3	$161.32	13.104%	$182.4594	$182.46	$182.45	$182.50
Purchase #4	$79.74	9.534%	$87.3424	$87.34	$87.35	$87.30
Purchase #5	$149.72	6.614%	$159.6225	$159.62	$159.60	$159.60
Purchase #6	$156.51	6.465%	$166.6284	$166.63	$166.65	$166.60
Purchase #7	$165.41	4.594%	$173.0089	$173.01	$173.00	$173.00
7 purchase totals =	$1,055.94		$1,155.5092	$1,155.50	$1,155.50	$1,155.40