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	$250.83	5.184%	$263.833	$263.83	$263.85	$263.80
Purchase #2	$221.72	3.356%	$229.1609	$229.16	$229.15	$229.20
Purchase #3	$112.64	13.840%	$128.2294	$128.23	$128.25	$128.20
Purchase #4	$73.69	6.373%	$78.3863	$78.39	$78.40	$78.40
Purchase #5	$30.75	11.541%	$34.2989	$34.30	$34.30	$34.30
Purchase #6	$14.48	6.593%	$15.4347	$15.43	$15.45	$15.40
Purchase #7	$46.36	12.774%	$52.282	$52.28	$52.30	$52.30
7 purchase totals =	$750.47		$801.6252	$801.62	$801.70	$801.60