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	$88.90	11.485%	$99.1102	$99.11	$99.10	$99.10
Purchase #2	$188.80	4.841%	$197.9398	$197.94	$197.95	$197.90
Purchase #3	$144.47	10.502%	$159.6422	$159.64	$159.65	$159.60
Purchase #4	$93.30	7.495%	$100.2928	$100.29	$100.30	$100.30
Purchase #5	$127.61	6.767%	$136.2454	$136.25	$136.25	$136.20
Purchase #6	$183.40	11.364%	$204.2416	$204.24	$204.25	$204.20
Purchase #7	$157.75	6.770%	$168.4297	$168.43	$168.45	$168.40
7 purchase totals =	$984.23		$1,065.9017	$1,065.90	$1,065.95	$1,065.70