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	$152.52	8.831%	$165.989	$165.99	$166.00	$166.00
Purchase #2	$211.39	5.146%	$222.2681	$222.27	$222.25	$222.30
Purchase #3	$219.89	3.666%	$227.9512	$227.95	$227.95	$228.00
Purchase #4	$169.30	13.681%	$192.4619	$192.46	$192.45	$192.50
Purchase #5	$197.95	13.608%	$224.887	$224.89	$224.90	$224.90
Purchase #6	$135.38	12.502%	$152.3052	$152.31	$152.30	$152.30
Purchase #7	$225.76	7.114%	$241.8206	$241.82	$241.80	$241.80
7 purchase totals =	$1,312.19		$1,427.6830	$1,427.69	$1,427.65	$1,427.80