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	$240.37	12.815%	$271.1734	$271.17	$271.15	$271.20
Purchase #2	$242.95	13.150%	$274.8979	$274.90	$274.90	$274.90
Purchase #3	$208.90	3.524%	$216.2616	$216.26	$216.25	$216.30
Purchase #4	$67.90	12.683%	$76.5118	$76.51	$76.50	$76.50
Purchase #5	$56.55	7.191%	$60.6165	$60.62	$60.60	$60.60
Purchase #6	$131.97	7.792%	$142.2531	$142.25	$142.25	$142.30
Purchase #7	$243.78	4.671%	$255.167	$255.17	$255.15	$255.20
7 purchase totals =	$1,192.42		$1,296.8813	$1,296.88	$1,296.80	$1,297.00