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	$140.89	7.396%	$151.3102	$151.31	$151.30	$151.30
Purchase #2	$214.84	10.837%	$238.1222	$238.12	$238.10	$238.10
Purchase #3	$63.80	8.621%	$69.3002	$69.30	$69.30	$69.30
Purchase #4	$185.83	10.604%	$205.5354	$205.54	$205.55	$205.50
Purchase #5	$27.49	8.543%	$29.8385	$29.84	$29.85	$29.80
Purchase #6	$71.82	8.828%	$78.1603	$78.16	$78.15	$78.20
Purchase #7	$56.37	9.430%	$61.6857	$61.69	$61.70	$61.70
7 purchase totals =	$761.04		$833.9525	$833.96	$833.95	$833.90