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	$48.33	6.515%	$51.4787	$51.48	$51.50	$51.50
Purchase #2	$243.85	4.742%	$255.4134	$255.41	$255.40	$255.40
Purchase #3	$44.72	8.760%	$48.6375	$48.64	$48.65	$48.60
Purchase #4	$147.40	7.278%	$158.1278	$158.13	$158.15	$158.10
Purchase #5	$225.38	4.785%	$236.1644	$236.16	$236.15	$236.20
Purchase #6	$101.74	11.845%	$113.7911	$113.79	$113.80	$113.80
Purchase #7	$202.35	9.370%	$221.3102	$221.31	$221.30	$221.30
7 purchase totals =	$1,013.77		$1,084.9231	$1,084.92	$1,084.95	$1,084.90