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	$55.94	6.487%	$59.5688	$59.57	$59.55	$59.60
Purchase #2	$230.32	7.688%	$248.027	$248.03	$248.05	$248.00
Purchase #3	$32.73	4.650%	$34.2519	$34.25	$34.25	$34.30
Purchase #4	$16.86	9.343%	$18.4352	$18.44	$18.45	$18.40
Purchase #5	$38.36	3.172%	$39.5768	$39.58	$39.60	$39.60
Purchase #6	$54.85	4.516%	$57.327	$57.33	$57.35	$57.30
Purchase #7	$122.41	13.713%	$139.1961	$139.20	$139.20	$139.20
7 purchase totals =	$551.47		$596.3828	$596.40	$596.45	$596.40