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	$165.36	4.168%	$172.2522	$172.25	$172.25	$172.30
Purchase #2	$117.35	6.306%	$124.7501	$124.75	$124.75	$124.80
Purchase #3	$156.93	9.857%	$172.3986	$172.40	$172.40	$172.40
Purchase #4	$142.93	8.125%	$154.5431	$154.54	$154.55	$154.50
Purchase #5	$169.73	6.573%	$180.8864	$180.89	$180.90	$180.90
Purchase #6	$213.34	13.249%	$241.6054	$241.61	$241.60	$241.60
Purchase #7	$96.30	12.773%	$108.6004	$108.60	$108.60	$108.60
7 purchase totals =	$1,061.94		$1,155.0362	$1,155.04	$1,155.05	$1,155.10