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	$33.77	7.529%	$36.3125	$36.31	$36.30	$36.30
Purchase #2	$145.61	13.521%	$165.2979	$165.30	$165.30	$165.30
Purchase #3	$52.56	12.345%	$59.0485	$59.05	$59.05	$59.00
Purchase #4	$50.47	11.693%	$56.3715	$56.37	$56.35	$56.40
Purchase #5	$6.88	13.459%	$7.806	$7.81	$7.80	$7.80
Purchase #6	$217.57	10.766%	$240.9936	$240.99	$241.00	$241.00
Purchase #7	$196.32	5.863%	$207.8302	$207.83	$207.85	$207.80
7 purchase totals =	$703.18		$773.6602	$773.66	$773.65	$773.60