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	$246.29	11.503%	$274.6207	$274.62	$274.60	$274.60
Purchase #2	$144.37	11.136%	$160.447	$160.45	$160.45	$160.40
Purchase #3	$111.37	11.297%	$123.9515	$123.95	$123.95	$124.00
Purchase #4	$89.81	10.517%	$99.2553	$99.26	$99.25	$99.30
Purchase #5	$214.61	4.329%	$223.9005	$223.90	$223.90	$223.90
Purchase #6	$98.74	8.728%	$107.358	$107.36	$107.35	$107.40
Purchase #7	$89.61	11.430%	$99.8524	$99.85	$99.85	$99.90
7 purchase totals =	$994.80		$1,089.3854	$1,089.39	$1,089.35	$1,089.50