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	$171.36	4.235%	$178.6171	$178.62	$178.60	$178.60
Purchase #2	$154.70	6.505%	$164.7632	$164.76	$164.75	$164.80
Purchase #3	$79.70	11.841%	$89.1373	$89.14	$89.15	$89.10
Purchase #4	$89.91	8.115%	$97.2062	$97.21	$97.20	$97.20
Purchase #5	$105.80	5.246%	$111.3503	$111.35	$111.35	$111.40
Purchase #6	$99.31	5.639%	$104.9101	$104.91	$104.90	$104.90
Purchase #7	$175.46	9.741%	$192.5516	$192.55	$192.55	$192.60
7 purchase totals =	$876.24		$938.5358	$938.54	$938.50	$938.60