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	$29.69	10.864%	$32.9155	$32.92	$32.90	$32.90
Purchase #2	$244.60	12.557%	$275.3144	$275.31	$275.30	$275.30
Purchase #3	$91.56	9.354%	$100.1245	$100.12	$100.10	$100.10
Purchase #4	$207.90	10.312%	$229.3386	$229.34	$229.35	$229.30
Purchase #5	$142.39	6.239%	$151.2737	$151.27	$151.25	$151.30
Purchase #6	$139.29	7.641%	$149.9331	$149.93	$149.95	$149.90
Purchase #7	$183.77	10.661%	$203.3617	$203.36	$203.35	$203.40
7 purchase totals =	$1,039.20		$1,142.2615	$1,142.25	$1,142.20	$1,142.20