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	$42.54	6.727%	$45.4017	$45.40	$45.40	$45.40
Purchase #2	$164.80	12.616%	$185.5912	$185.59	$185.60	$185.60
Purchase #3	$136.76	11.548%	$152.553	$152.55	$152.55	$152.60
Purchase #4	$38.83	4.842%	$40.7101	$40.71	$40.70	$40.70
Purchase #5	$23.63	7.769%	$25.4658	$25.47	$25.45	$25.50
Purchase #6	$42.36	13.489%	$48.0739	$48.07	$48.05	$48.10
Purchase #7	$170.87	11.110%	$189.8537	$189.85	$189.85	$189.90
7 purchase totals =	$619.79		$687.6494	$687.64	$687.60	$687.80