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	$111.88	3.510%	$115.807	$115.81	$115.80	$115.80
Purchase #2	$57.37	7.712%	$61.7944	$61.79	$61.80	$61.80
Purchase #3	$122.28	6.754%	$130.5388	$130.54	$130.55	$130.50
Purchase #4	$158.41	9.158%	$172.9172	$172.92	$172.90	$172.90
Purchase #5	$132.27	9.847%	$145.2946	$145.29	$145.30	$145.30
Purchase #6	$87.42	10.152%	$96.2949	$96.29	$96.30	$96.30
Purchase #7	$74.85	13.681%	$85.0902	$85.09	$85.10	$85.10
7 purchase totals =	$744.48		$807.7371	$807.73	$807.75	$807.70