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	$79.98	13.469%	$90.7525	$90.75	$90.75	$90.80
Purchase #2	$83.86	5.346%	$88.3432	$88.34	$88.35	$88.30
Purchase #3	$138.97	4.498%	$145.2209	$145.22	$145.20	$145.20
Purchase #4	$118.47	6.149%	$125.7547	$125.75	$125.75	$125.80
Purchase #5	$218.30	9.346%	$238.7023	$238.70	$238.70	$238.70
Purchase #6	$225.51	6.594%	$240.3801	$240.38	$240.40	$240.40
Purchase #7	$68.89	13.431%	$78.1426	$78.14	$78.15	$78.10
7 purchase totals =	$933.98		$1,007.2963	$1,007.28	$1,007.30	$1,007.30