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	$90.68	9.434%	$99.2348	$99.23	$99.25	$99.20
Purchase #2	$153.63	10.320%	$169.4846	$169.48	$169.50	$169.50
Purchase #3	$238.37	13.284%	$270.0351	$270.04	$270.05	$270.00
Purchase #4	$70.35	8.231%	$76.1405	$76.14	$76.15	$76.10
Purchase #5	$99.25	6.203%	$105.4065	$105.41	$105.40	$105.40
Purchase #6	$242.67	9.684%	$266.1702	$266.17	$266.15	$266.20
Purchase #7	$47.51	12.469%	$53.434	$53.43	$53.45	$53.40
7 purchase totals =	$942.46		$1,039.9057	$1,039.90	$1,039.95	$1,039.80