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	$40.44	4.576%	$42.2905	$42.29	$42.30	$42.30
Purchase #2	$67.83	7.343%	$72.8108	$72.81	$72.80	$72.80
Purchase #3	$69.80	3.213%	$72.0427	$72.04	$72.05	$72.00
Purchase #4	$208.26	12.127%	$233.5157	$233.52	$233.50	$233.50
Purchase #5	$218.32	11.196%	$242.7631	$242.76	$242.75	$242.80
Purchase #6	$138.95	13.729%	$158.0264	$158.03	$158.05	$158.00
Purchase #7	$105.60	8.749%	$114.8389	$114.84	$114.85	$114.80
7 purchase totals =	$849.20		$936.2881	$936.29	$936.30	$936.20