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	$57.27	12.209%	$64.2621	$64.26	$64.25	$64.30
Purchase #2	$198.47	4.256%	$206.9169	$206.92	$206.90	$206.90
Purchase #3	$91.76	13.731%	$104.3596	$104.36	$104.35	$104.40
Purchase #4	$118.86	7.452%	$127.7174	$127.72	$127.70	$127.70
Purchase #5	$223.42	9.261%	$244.1109	$244.11	$244.10	$244.10
Purchase #6	$111.77	10.832%	$123.8769	$123.88	$123.90	$123.90
Purchase #7	$202.46	3.336%	$209.2141	$209.21	$209.20	$209.20
7 purchase totals =	$1,004.01		$1,080.4579	$1,080.46	$1,080.40	$1,080.50