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	$57.31	3.860%	$59.5222	$59.52	$59.50	$59.50
Purchase #2	$69.67	8.114%	$75.323	$75.32	$75.30	$75.30
Purchase #3	$165.49	13.291%	$187.4853	$187.49	$187.50	$187.50
Purchase #4	$232.43	9.855%	$255.336	$255.34	$255.35	$255.30
Purchase #5	$151.28	6.504%	$161.1193	$161.12	$161.10	$161.10
Purchase #6	$144.44	11.302%	$160.7646	$160.76	$160.75	$160.80
Purchase #7	$160.55	12.703%	$180.9447	$180.94	$180.95	$180.90
7 purchase totals =	$981.17		$1,080.4951	$1,080.49	$1,080.45	$1,080.40