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	$138.25	9.559%	$151.4653	$151.47	$151.45	$151.50
Purchase #2	$78.92	12.269%	$88.6027	$88.60	$88.60	$88.60
Purchase #3	$152.92	8.599%	$166.0696	$166.07	$166.05	$166.10
Purchase #4	$59.59	12.595%	$67.0954	$67.10	$67.10	$67.10
Purchase #5	$72.86	7.615%	$78.4083	$78.41	$78.40	$78.40
Purchase #6	$134.47	7.283%	$144.2635	$144.26	$144.25	$144.30
Purchase #7	$129.32	11.686%	$144.4323	$144.43	$144.45	$144.40
7 purchase totals =	$766.33		$840.3371	$840.34	$840.30	$840.40