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	$82.96	9.205%	$90.5965	$90.60	$90.60	$90.60
Purchase #2	$90.35	5.637%	$95.443	$95.44	$95.45	$95.40
Purchase #3	$53.30	10.135%	$58.702	$58.70	$58.70	$58.70
Purchase #4	$7.32	10.114%	$8.0603	$8.06	$8.05	$8.10
Purchase #5	$156.29	10.198%	$172.2285	$172.23	$172.25	$172.20
Purchase #6	$27.32	4.558%	$28.5652	$28.57	$28.55	$28.60
Purchase #7	$66.91	4.364%	$69.83	$69.83	$69.85	$69.80
7 purchase totals =	$484.45		$523.4255	$523.43	$523.45	$523.40