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	$94.49	5.276%	$99.4753	$99.48	$99.50	$99.50
Purchase #2	$131.72	9.333%	$144.0134	$144.01	$144.00	$144.00
Purchase #3	$231.91	6.425%	$246.8102	$246.81	$246.80	$246.80
Purchase #4	$248.58	10.673%	$275.1109	$275.11	$275.10	$275.10
Purchase #5	$172.59	8.394%	$187.0772	$187.08	$187.10	$187.10
Purchase #6	$141.76	4.738%	$148.4766	$148.48	$148.50	$148.50
Purchase #7	$111.57	8.538%	$121.0958	$121.10	$121.10	$121.10
7 purchase totals =	$1,132.62		$1,222.0594	$1,222.07	$1,222.10	$1,222.10