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	$86.77	4.389%	$90.5783	$90.58	$90.60	$90.60
Purchase #2	$131.82	4.558%	$137.8284	$137.83	$137.85	$137.80
Purchase #3	$229.40	9.549%	$251.3054	$251.31	$251.30	$251.30
Purchase #4	$71.45	12.636%	$80.4784	$80.48	$80.50	$80.50
Purchase #5	$91.55	9.265%	$100.0321	$100.03	$100.05	$100.00
Purchase #6	$181.39	6.255%	$192.7359	$192.74	$192.75	$192.70
Purchase #7	$210.51	9.781%	$231.1	$231.10	$231.10	$231.10
7 purchase totals =	$1,002.89		$1,084.0585	$1,084.07	$1,084.15	$1,084.00