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	$222.86	13.585%	$253.1355	$253.14	$253.15	$253.10
Purchase #2	$85.35	7.168%	$91.4679	$91.47	$91.45	$91.50
Purchase #3	$154.71	8.554%	$167.9439	$167.94	$167.95	$167.90
Purchase #4	$141.82	8.790%	$154.286	$154.29	$154.30	$154.30
Purchase #5	$89.73	13.740%	$102.0589	$102.06	$102.05	$102.10
Purchase #6	$94.74	5.687%	$100.1279	$100.13	$100.15	$100.10
Purchase #7	$23.30	10.149%	$25.6647	$25.66	$25.65	$25.70
7 purchase totals =	$812.51		$894.6848	$894.69	$894.70	$894.70