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	$79.30	7.257%	$85.0548	$85.05	$85.05	$85.10
Purchase #2	$91.62	3.160%	$94.5152	$94.52	$94.50	$94.50
Purchase #3	$69.37	3.334%	$71.6828	$71.68	$71.70	$71.70
Purchase #4	$228.56	12.546%	$257.2351	$257.24	$257.25	$257.20
Purchase #5	$39.89	5.753%	$42.1849	$42.18	$42.20	$42.20
Purchase #6	$216.77	10.759%	$240.0923	$240.09	$240.10	$240.10
Purchase #7	$107.96	3.491%	$111.7289	$111.73	$111.75	$111.70
7 purchase totals =	$833.47		$902.4940	$902.49	$902.55	$902.50