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	$57.80	3.119%	$59.6028	$59.60	$59.60	$59.60
Purchase #2	$145.31	7.761%	$156.5875	$156.59	$156.60	$156.60
Purchase #3	$153.53	7.250%	$164.6609	$164.66	$164.65	$164.70
Purchase #4	$10.48	13.685%	$11.9142	$11.91	$11.90	$11.90
Purchase #5	$148.80	8.126%	$160.8915	$160.89	$160.90	$160.90
Purchase #6	$75.36	13.650%	$85.6466	$85.65	$85.65	$85.60
Purchase #7	$11.65	4.674%	$12.1945	$12.19	$12.20	$12.20
7 purchase totals =	$602.93		$651.4980	$651.49	$651.50	$651.50