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	$94.32	6.427%	$100.3819	$100.38	$100.40	$100.40
Purchase #2	$48.78	12.848%	$55.0473	$55.05	$55.05	$55.00
Purchase #3	$157.39	7.492%	$169.1817	$169.18	$169.20	$169.20
Purchase #4	$19.53	3.208%	$20.1565	$20.16	$20.15	$20.20
Purchase #5	$214.32	10.171%	$236.1185	$236.12	$236.10	$236.10
Purchase #6	$54.55	13.292%	$61.8008	$61.80	$61.80	$61.80
Purchase #7	$116.86	3.453%	$120.8952	$120.90	$120.90	$120.90
7 purchase totals =	$705.75		$763.5819	$763.59	$763.60	$763.60