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	$50.51	12.406%	$56.7763	$56.78	$56.80	$56.80
Purchase #2	$12.35	5.532%	$13.0332	$13.03	$13.05	$13.00
Purchase #3	$39.43	8.363%	$42.7275	$42.73	$42.75	$42.70
Purchase #4	$178.38	12.245%	$200.2226	$200.22	$200.20	$200.20
Purchase #5	$206.50	3.642%	$214.0207	$214.02	$214.00	$214.00
Purchase #6	$20.72	5.655%	$21.8917	$21.89	$21.90	$21.90
Purchase #7	$170.67	6.769%	$182.2227	$182.22	$182.20	$182.20
7 purchase totals =	$678.56		$730.8947	$730.89	$730.90	$730.80