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	$248.55	8.645%	$270.0371	$270.04	$270.05	$270.00
Purchase #2	$146.90	8.167%	$158.8973	$158.90	$158.90	$158.90
Purchase #3	$175.64	6.648%	$187.3165	$187.32	$187.30	$187.30
Purchase #4	$132.48	7.634%	$142.5935	$142.59	$142.60	$142.60
Purchase #5	$185.95	9.607%	$203.8142	$203.81	$203.80	$203.80
Purchase #6	$105.50	13.377%	$119.6127	$119.61	$119.60	$119.60
Purchase #7	$37.68	9.404%	$41.2234	$41.22	$41.20	$41.20
7 purchase totals =	$1,032.70		$1,123.4947	$1,123.49	$1,123.45	$1,123.40