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	$52.26	6.242%	$55.5221	$55.52	$55.50	$55.50
Purchase #2	$61.77	8.721%	$67.157	$67.16	$67.15	$67.20
Purchase #3	$248.81	10.855%	$275.8183	$275.82	$275.80	$275.80
Purchase #4	$248.25	9.402%	$271.5905	$271.59	$271.60	$271.60
Purchase #5	$59.55	3.586%	$61.6855	$61.69	$61.70	$61.70
Purchase #6	$105.39	13.307%	$119.4142	$119.41	$119.40	$119.40
Purchase #7	$133.77	6.442%	$142.3875	$142.39	$142.40	$142.40
7 purchase totals =	$909.80		$993.5751	$993.58	$993.55	$993.60