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	$80.25	11.625%	$89.5791	$89.58	$89.60	$89.60
Purchase #2	$66.73	4.356%	$69.6368	$69.64	$69.65	$69.60
Purchase #3	$223.38	11.837%	$249.8215	$249.82	$249.80	$249.80
Purchase #4	$22.67	3.742%	$23.5183	$23.52	$23.50	$23.50
Purchase #5	$44.93	9.756%	$49.3134	$49.31	$49.30	$49.30
Purchase #6	$34.67	6.405%	$36.8906	$36.89	$36.90	$36.90
Purchase #7	$12.28	11.739%	$13.7215	$13.72	$13.70	$13.70
7 purchase totals =	$484.91		$532.4812	$532.48	$532.45	$532.40