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	$31.31	3.795%	$32.4982	$32.50	$32.50	$32.50
Purchase #2	$34.52	7.867%	$37.2357	$37.24	$37.25	$37.20
Purchase #3	$135.53	10.727%	$150.0683	$150.07	$150.05	$150.10
Purchase #4	$201.86	13.739%	$229.5935	$229.59	$229.60	$229.60
Purchase #5	$230.50	9.772%	$253.0245	$253.02	$253.00	$253.00
Purchase #6	$6.86	10.405%	$7.5738	$7.57	$7.55	$7.60
Purchase #7	$64.61	13.561%	$73.3718	$73.37	$73.35	$73.40
7 purchase totals =	$705.19		$783.3658	$783.36	$783.30	$783.40