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	$55.63	7.363%	$59.726	$59.73	$59.75	$59.70
Purchase #2	$48.74	3.545%	$50.4678	$50.47	$50.45	$50.50
Purchase #3	$92.25	8.149%	$99.7675	$99.77	$99.75	$99.80
Purchase #4	$125.88	13.609%	$143.011	$143.01	$143.00	$143.00
Purchase #5	$111.54	7.506%	$119.9122	$119.91	$119.90	$119.90
Purchase #6	$156.67	4.366%	$163.5102	$163.51	$163.50	$163.50
Purchase #7	$10.37	5.277%	$10.9172	$10.92	$10.90	$10.90
7 purchase totals =	$601.08		$647.3119	$647.32	$647.25	$647.30