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	$14.82	7.130%	$15.8767	$15.88	$15.90	$15.90
Purchase #2	$29.61	9.690%	$32.4792	$32.48	$32.50	$32.50
Purchase #3	$105.52	5.366%	$111.1822	$111.18	$111.20	$111.20
Purchase #4	$196.29	4.252%	$204.6363	$204.64	$204.65	$204.60
Purchase #5	$219.98	11.478%	$245.2293	$245.23	$245.25	$245.20
Purchase #6	$208.72	10.124%	$229.8508	$229.85	$229.85	$229.90
Purchase #7	$181.45	11.675%	$202.6343	$202.63	$202.65	$202.60
7 purchase totals =	$956.39		$1,041.8888	$1,041.89	$1,042.00	$1,041.90