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	$143.88	4.414%	$150.2309	$150.23	$150.25	$150.20
Purchase #2	$231.78	11.669%	$258.8264	$258.83	$258.85	$258.80
Purchase #3	$173.35	10.805%	$192.0805	$192.08	$192.10	$192.10
Purchase #4	$83.90	6.523%	$89.3728	$89.37	$89.35	$89.40
Purchase #5	$202.56	4.187%	$211.0412	$211.04	$211.05	$211.00
Purchase #6	$207.70	7.564%	$223.4104	$223.41	$223.40	$223.40
Purchase #7	$34.49	9.361%	$37.7186	$37.72	$37.70	$37.70
7 purchase totals =	$1,077.66		$1,162.6808	$1,162.68	$1,162.70	$1,162.60