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	$233.33	3.535%	$241.5782	$241.58	$241.60	$241.60
Purchase #2	$137.88	3.155%	$142.2301	$142.23	$142.25	$142.20
Purchase #3	$174.27	9.501%	$190.8274	$190.83	$190.85	$190.80
Purchase #4	$226.76	5.273%	$238.7171	$238.72	$238.70	$238.70
Purchase #5	$166.73	5.266%	$175.51	$175.51	$175.50	$175.50
Purchase #6	$199.45	8.598%	$216.5987	$216.60	$216.60	$216.60
Purchase #7	$68.31	13.181%	$77.3139	$77.31	$77.30	$77.30
7 purchase totals =	$1,206.73		$1,282.7754	$1,282.78	$1,282.80	$1,282.70