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	$70.25	3.761%	$72.8921	$72.89	$72.90	$72.90
Purchase #2	$248.62	10.265%	$274.1408	$274.14	$274.15	$274.10
Purchase #3	$229.50	6.451%	$244.305	$244.31	$244.30	$244.30
Purchase #4	$55.70	11.212%	$61.9451	$61.95	$61.95	$61.90
Purchase #5	$93.61	11.357%	$104.2413	$104.24	$104.25	$104.20
Purchase #6	$63.40	10.471%	$70.0386	$70.04	$70.05	$70.00
Purchase #7	$46.68	13.151%	$52.8189	$52.82	$52.80	$52.80
7 purchase totals =	$807.76		$880.3818	$880.39	$880.40	$880.20