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	$21.66	4.480%	$22.6304	$22.63	$22.65	$22.60
Purchase #2	$191.29	5.628%	$202.0558	$202.06	$202.05	$202.10
Purchase #3	$85.85	3.681%	$89.0101	$89.01	$89.00	$89.00
Purchase #4	$154.48	13.562%	$175.4306	$175.43	$175.45	$175.40
Purchase #5	$137.50	10.617%	$152.0984	$152.10	$152.10	$152.10
Purchase #6	$155.94	10.574%	$172.4291	$172.43	$172.45	$172.40
Purchase #7	$244.52	12.786%	$275.7843	$275.78	$275.80	$275.80
7 purchase totals =	$991.24		$1,089.4387	$1,089.44	$1,089.50	$1,089.40