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	$154.35	11.183%	$171.611	$171.61	$171.60	$171.60
Purchase #2	$230.85	13.286%	$261.5207	$261.52	$261.50	$261.50
Purchase #3	$71.98	8.427%	$78.0458	$78.05	$78.05	$78.00
Purchase #4	$61.81	8.572%	$67.1084	$67.11	$67.10	$67.10
Purchase #5	$19.89	11.486%	$22.1746	$22.17	$22.15	$22.20
Purchase #6	$225.96	7.744%	$243.4583	$243.46	$243.45	$243.50
Purchase #7	$33.80	10.475%	$37.3406	$37.34	$37.35	$37.30
7 purchase totals =	$798.64		$881.2594	$881.26	$881.20	$881.20