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	$206.50	8.367%	$223.7779	$223.78	$223.80	$223.80
Purchase #2	$50.40	7.721%	$54.2914	$54.29	$54.30	$54.30
Purchase #3	$172.63	13.470%	$195.8833	$195.88	$195.90	$195.90
Purchase #4	$124.29	9.683%	$136.325	$136.33	$136.35	$136.30
Purchase #5	$225.49	8.486%	$244.6251	$244.63	$244.65	$244.60
Purchase #6	$89.99	11.553%	$100.3865	$100.39	$100.40	$100.40
Purchase #7	$16.52	9.533%	$18.0949	$18.09	$18.10	$18.10
7 purchase totals =	$885.82		$973.3841	$973.39	$973.50	$973.40