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	$173.59	5.703%	$183.4898	$183.49	$183.50	$183.50
Purchase #2	$190.40	6.185%	$202.1762	$202.18	$202.20	$202.20
Purchase #3	$28.90	7.827%	$31.162	$31.16	$31.15	$31.20
Purchase #4	$136.59	4.362%	$142.5481	$142.55	$142.55	$142.50
Purchase #5	$134.62	13.577%	$152.8974	$152.90	$152.90	$152.90
Purchase #6	$13.27	6.187%	$14.091	$14.09	$14.10	$14.10
Purchase #7	$243.38	3.727%	$252.4508	$252.45	$252.45	$252.50
7 purchase totals =	$920.75		$978.8153	$978.82	$978.85	$978.90