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	$82.54	6.811%	$88.1618	$88.16	$88.15	$88.20
Purchase #2	$77.32	7.691%	$83.2667	$83.27	$83.25	$83.30
Purchase #3	$143.76	4.533%	$150.2766	$150.28	$150.30	$150.30
Purchase #4	$143.71	10.523%	$158.8326	$158.83	$158.85	$158.80
Purchase #5	$179.47	4.482%	$187.5138	$187.51	$187.50	$187.50
Purchase #6	$36.93	3.563%	$38.2458	$38.25	$38.25	$38.20
Purchase #7	$226.72	4.479%	$236.8748	$236.87	$236.85	$236.90
7 purchase totals =	$890.45		$943.1721	$943.17	$943.15	$943.20