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	$83.94	5.630%	$88.6658	$88.67	$88.65	$88.70
Purchase #2	$221.44	9.253%	$241.9298	$241.93	$241.95	$241.90
Purchase #3	$214.30	13.595%	$243.4341	$243.43	$243.45	$243.40
Purchase #4	$72.64	13.740%	$82.6207	$82.62	$82.60	$82.60
Purchase #5	$137.86	6.329%	$146.5852	$146.59	$146.60	$146.60
Purchase #6	$29.69	11.649%	$33.1486	$33.15	$33.15	$33.10
Purchase #7	$138.63	9.472%	$151.761	$151.76	$151.75	$151.80
7 purchase totals =	$898.50		$988.1452	$988.15	$988.15	$988.10