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	$80.64	13.862%	$91.8183	$91.82	$91.80	$91.80
Purchase #2	$17.50	5.217%	$18.413	$18.41	$18.40	$18.40
Purchase #3	$185.54	7.161%	$198.8265	$198.83	$198.85	$198.80
Purchase #4	$151.94	13.860%	$172.9989	$173.00	$173.00	$173.00
Purchase #5	$214.32	6.142%	$227.4835	$227.48	$227.50	$227.50
Purchase #6	$107.49	9.690%	$117.9058	$117.91	$117.90	$117.90
Purchase #7	$96.40	5.731%	$101.9247	$101.92	$101.90	$101.90
7 purchase totals =	$853.83		$929.3707	$929.37	$929.35	$929.30