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	$123.69	4.211%	$128.8986	$128.90	$128.90	$128.90
Purchase #2	$97.25	8.143%	$105.1691	$105.17	$105.15	$105.20
Purchase #3	$107.33	9.408%	$117.4276	$117.43	$117.45	$117.40
Purchase #4	$236.51	6.330%	$251.4811	$251.48	$251.50	$251.50
Purchase #5	$244.40	8.111%	$264.2233	$264.22	$264.20	$264.20
Purchase #6	$108.71	3.702%	$112.7344	$112.73	$112.75	$112.70
Purchase #7	$98.42	5.232%	$103.5693	$103.57	$103.55	$103.60
7 purchase totals =	$1,016.31		$1,083.5034	$1,083.50	$1,083.50	$1,083.50