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	$134.51	12.409%	$151.2013	$151.20	$151.20	$151.20
Purchase #2	$192.49	4.319%	$200.8036	$200.80	$200.80	$200.80
Purchase #3	$112.60	10.502%	$124.4253	$124.43	$124.45	$124.40
Purchase #4	$105.52	4.108%	$109.8548	$109.85	$109.85	$109.90
Purchase #5	$222.26	12.490%	$250.0203	$250.02	$250.00	$250.00
Purchase #6	$158.25	5.645%	$167.1832	$167.18	$167.20	$167.20
Purchase #7	$74.45	5.216%	$78.3333	$78.33	$78.35	$78.30
7 purchase totals =	$1,000.08		$1,081.8218	$1,081.81	$1,081.85	$1,081.80