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	$20.48	3.635%	$21.2244	$21.22	$21.20	$21.20
Purchase #2	$82.77	8.464%	$89.7757	$89.78	$89.80	$89.80
Purchase #3	$10.46	12.741%	$11.7927	$11.79	$11.80	$11.80
Purchase #4	$161.27	11.160%	$179.2677	$179.27	$179.25	$179.30
Purchase #5	$20.25	5.465%	$21.3567	$21.36	$21.35	$21.40
Purchase #6	$248.28	3.718%	$257.5111	$257.51	$257.50	$257.50
Purchase #7	$168.89	3.448%	$174.7133	$174.71	$174.70	$174.70
7 purchase totals =	$712.40		$755.6416	$755.64	$755.60	$755.70