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	$63.25	11.284%	$70.3871	$70.39	$70.40	$70.40
Purchase #2	$46.26	8.869%	$50.3628	$50.36	$50.35	$50.40
Purchase #3	$157.93	6.654%	$168.4387	$168.44	$168.45	$168.40
Purchase #4	$173.26	13.647%	$196.9048	$196.90	$196.90	$196.90
Purchase #5	$159.58	12.863%	$180.1068	$180.11	$180.10	$180.10
Purchase #6	$75.96	7.420%	$81.5962	$81.60	$81.60	$81.60
Purchase #7	$230.31	10.499%	$254.4902	$254.49	$254.50	$254.50
7 purchase totals =	$906.55		$1,002.2866	$1,002.29	$1,002.30	$1,002.30