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	$189.90	3.500%	$196.5465	$196.55	$196.55	$196.50
Purchase #2	$158.62	7.663%	$170.7751	$170.78	$170.80	$170.80
Purchase #3	$72.37	8.720%	$78.6807	$78.68	$78.70	$78.70
Purchase #4	$11.90	8.382%	$12.8975	$12.90	$12.90	$12.90
Purchase #5	$52.32	12.244%	$58.7261	$58.73	$58.75	$58.70
Purchase #6	$18.25	12.632%	$20.5553	$20.56	$20.55	$20.60
Purchase #7	$40.99	3.471%	$42.4128	$42.41	$42.40	$42.40
7 purchase totals =	$544.35		$580.5940	$580.61	$580.65	$580.60