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	$239.54	6.628%	$255.4167	$255.42	$255.40	$255.40
Purchase #2	$18.35	3.675%	$19.0244	$19.02	$19.00	$19.00
Purchase #3	$127.86	6.777%	$136.5251	$136.53	$136.55	$136.50
Purchase #4	$59.38	12.650%	$66.8916	$66.89	$66.90	$66.90
Purchase #5	$60.62	13.120%	$68.5733	$68.57	$68.55	$68.60
Purchase #6	$27.27	13.702%	$31.0065	$31.01	$31.00	$31.00
Purchase #7	$158.52	7.283%	$170.065	$170.07	$170.05	$170.10
7 purchase totals =	$691.54		$747.5026	$747.51	$747.45	$747.50