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	$11.29	3.476%	$11.6824	$11.68	$11.70	$11.70
Purchase #2	$101.99	9.424%	$111.6015	$111.60	$111.60	$111.60
Purchase #3	$37.37	7.337%	$40.1118	$40.11	$40.10	$40.10
Purchase #4	$82.78	9.329%	$90.5025	$90.50	$90.50	$90.50
Purchase #5	$160.93	13.661%	$182.9146	$182.91	$182.90	$182.90
Purchase #6	$97.79	6.583%	$104.2275	$104.23	$104.25	$104.20
Purchase #7	$243.44	12.836%	$274.688	$274.69	$274.70	$274.70
7 purchase totals =	$735.59		$815.7283	$815.72	$815.75	$815.70