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	$232.58	6.301%	$247.2349	$247.23	$247.25	$247.20
Purchase #2	$114.37	8.267%	$123.825	$123.83	$123.85	$123.80
Purchase #3	$156.95	13.433%	$178.0331	$178.03	$178.05	$178.00
Purchase #4	$149.56	10.626%	$165.4522	$165.45	$165.45	$165.50
Purchase #5	$26.89	5.762%	$28.4394	$28.44	$28.45	$28.40
Purchase #6	$241.39	10.206%	$266.0263	$266.03	$266.05	$266.00
Purchase #7	$131.82	3.476%	$136.4021	$136.40	$136.40	$136.40
7 purchase totals =	$1,053.56		$1,145.4130	$1,145.41	$1,145.50	$1,145.30