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	$170.95	6.241%	$181.619	$181.62	$181.60	$181.60
Purchase #2	$104.45	11.852%	$116.8294	$116.83	$116.85	$116.80
Purchase #3	$167.85	3.616%	$173.9195	$173.92	$173.90	$173.90
Purchase #4	$115.37	4.541%	$120.609	$120.61	$120.60	$120.60
Purchase #5	$47.52	7.674%	$51.1667	$51.17	$51.15	$51.20
Purchase #6	$54.40	6.473%	$57.9213	$57.92	$57.90	$57.90
Purchase #7	$86.66	4.389%	$90.4635	$90.46	$90.45	$90.50
7 purchase totals =	$747.20		$792.5284	$792.53	$792.45	$792.50