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	$28.52	12.118%	$31.9761	$31.98	$32.00	$32.00
Purchase #2	$81.91	11.261%	$91.1339	$91.13	$91.15	$91.10
Purchase #3	$60.86	8.861%	$66.2528	$66.25	$66.25	$66.30
Purchase #4	$146.64	5.214%	$154.2858	$154.29	$154.30	$154.30
Purchase #5	$18.26	13.741%	$20.7691	$20.77	$20.75	$20.80
Purchase #6	$240.91	5.841%	$254.9816	$254.98	$255.00	$255.00
Purchase #7	$162.59	10.568%	$179.7725	$179.77	$179.75	$179.80
7 purchase totals =	$739.69		$799.1718	$799.17	$799.20	$799.30