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	$132.89	3.814%	$137.9584	$137.96	$137.95	$138.00
Purchase #2	$59.48	11.191%	$66.1364	$66.14	$66.15	$66.10
Purchase #3	$17.92	10.618%	$19.8227	$19.82	$19.80	$19.80
Purchase #4	$113.51	4.708%	$118.8541	$118.85	$118.85	$118.90
Purchase #5	$241.75	9.499%	$264.7138	$264.71	$264.70	$264.70
Purchase #6	$23.39	10.803%	$25.9168	$25.92	$25.90	$25.90
Purchase #7	$139.55	4.540%	$145.8856	$145.89	$145.90	$145.90
7 purchase totals =	$728.49		$779.2878	$779.29	$779.25	$779.30