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	$145.87	6.338%	$155.1152	$155.12	$155.10	$155.10
Purchase #2	$166.59	5.745%	$176.1606	$176.16	$176.15	$176.20
Purchase #3	$39.38	8.166%	$42.5958	$42.60	$42.60	$42.60
Purchase #4	$34.93	6.157%	$37.0806	$37.08	$37.10	$37.10
Purchase #5	$94.65	11.165%	$105.2177	$105.22	$105.20	$105.20
Purchase #6	$84.58	7.854%	$91.2229	$91.22	$91.20	$91.20
Purchase #7	$166.48	5.142%	$175.0404	$175.04	$175.05	$175.00
7 purchase totals =	$732.48		$782.4332	$782.44	$782.40	$782.40