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	$95.54	9.370%	$104.4921	$104.49	$104.50	$104.50
Purchase #2	$106.76	7.523%	$114.7916	$114.79	$114.80	$114.80
Purchase #3	$169.46	8.623%	$184.0725	$184.07	$184.05	$184.10
Purchase #4	$104.75	6.741%	$111.8112	$111.81	$111.80	$111.80
Purchase #5	$45.38	6.398%	$48.2834	$48.28	$48.30	$48.30
Purchase #6	$14.92	3.869%	$15.4973	$15.50	$15.50	$15.50
Purchase #7	$248.43	6.312%	$264.1109	$264.11	$264.10	$264.10
7 purchase totals =	$785.24		$843.0590	$843.05	$843.05	$843.10