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	$89.78	5.350%	$94.5832	$94.58	$94.60	$94.60
Purchase #2	$162.49	10.490%	$179.5352	$179.54	$179.55	$179.50
Purchase #3	$247.57	13.715%	$281.5242	$281.52	$281.50	$281.50
Purchase #4	$131.54	3.839%	$136.5898	$136.59	$136.60	$136.60
Purchase #5	$49.60	3.284%	$51.2289	$51.23	$51.25	$51.20
Purchase #6	$18.98	11.458%	$21.1547	$21.15	$21.15	$21.20
Purchase #7	$39.49	8.314%	$42.7732	$42.77	$42.75	$42.80
7 purchase totals =	$739.45		$807.3892	$807.38	$807.40	$807.40