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	$137.39	10.250%	$151.4725	$151.47	$151.45	$151.50
Purchase #2	$35.38	13.616%	$40.1973	$40.20	$40.20	$40.20
Purchase #3	$224.90	10.672%	$248.9013	$248.90	$248.90	$248.90
Purchase #4	$26.62	7.131%	$28.5183	$28.52	$28.50	$28.50
Purchase #5	$60.74	11.198%	$67.5417	$67.54	$67.55	$67.50
Purchase #6	$153.82	9.420%	$168.3098	$168.31	$168.30	$168.30
Purchase #7	$204.32	7.576%	$219.7993	$219.80	$219.80	$219.80
7 purchase totals =	$843.17		$924.7402	$924.74	$924.70	$924.70