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	$150.73	6.485%	$160.5048	$160.50	$160.50	$160.50
Purchase #2	$91.99	9.363%	$100.603	$100.60	$100.60	$100.60
Purchase #3	$142.59	3.126%	$147.0474	$147.05	$147.05	$147.00
Purchase #4	$15.38	5.860%	$16.2813	$16.28	$16.30	$16.30
Purchase #5	$52.69	3.192%	$54.3719	$54.37	$54.35	$54.40
Purchase #6	$207.42	13.250%	$234.9032	$234.90	$234.90	$234.90
Purchase #7	$101.45	8.308%	$109.8785	$109.88	$109.90	$109.90
7 purchase totals =	$762.25		$823.5901	$823.58	$823.60	$823.60