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	$56.26	6.401%	$59.8612	$59.86	$59.85	$59.90
Purchase #2	$50.90	13.721%	$57.884	$57.88	$57.90	$57.90
Purchase #3	$74.86	6.274%	$79.5567	$79.56	$79.55	$79.60
Purchase #4	$87.45	3.300%	$90.3359	$90.34	$90.35	$90.30
Purchase #5	$249.39	11.296%	$277.5611	$277.56	$277.55	$277.60
Purchase #6	$7.65	6.680%	$8.161	$8.16	$8.15	$8.20
Purchase #7	$21.63	8.771%	$23.5272	$23.53	$23.55	$23.50
7 purchase totals =	$548.14		$596.8871	$596.89	$596.90	$597.00