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	$39.30	7.246%	$42.1477	$42.15	$42.15	$42.10
Purchase #2	$145.30	3.772%	$150.7807	$150.78	$150.80	$150.80
Purchase #3	$21.52	8.112%	$23.2657	$23.27	$23.25	$23.30
Purchase #4	$42.99	13.806%	$48.9252	$48.93	$48.95	$48.90
Purchase #5	$59.25	3.245%	$61.1727	$61.17	$61.15	$61.20
Purchase #6	$60.25	4.815%	$63.151	$63.15	$63.15	$63.20
Purchase #7	$31.77	6.109%	$33.7108	$33.71	$33.70	$33.70
7 purchase totals =	$400.38		$423.1538	$423.16	$423.15	$423.20