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	$223.94	10.800%	$248.1255	$248.13	$248.15	$248.10
Purchase #2	$53.89	4.256%	$56.1836	$56.18	$56.20	$56.20
Purchase #3	$102.79	4.588%	$107.506	$107.51	$107.50	$107.50
Purchase #4	$91.34	11.391%	$101.7445	$101.74	$101.75	$101.70
Purchase #5	$132.90	11.512%	$148.1994	$148.20	$148.20	$148.20
Purchase #6	$175.34	5.774%	$185.4641	$185.46	$185.45	$185.50
Purchase #7	$30.69	8.603%	$33.3303	$33.33	$33.35	$33.30
7 purchase totals =	$810.89		$880.5534	$880.55	$880.60	$880.50