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	$11.32	9.510%	$12.3965	$12.40	$12.40	$12.40
Purchase #2	$156.77	8.732%	$170.4592	$170.46	$170.45	$170.50
Purchase #3	$127.76	4.813%	$133.9091	$133.91	$133.90	$133.90
Purchase #4	$6.64	13.412%	$7.5306	$7.53	$7.55	$7.50
Purchase #5	$49.50	8.542%	$53.7283	$53.73	$53.75	$53.70
Purchase #6	$66.78	3.814%	$69.327	$69.33	$69.35	$69.30
Purchase #7	$48.86	9.466%	$53.4851	$53.49	$53.50	$53.50
7 purchase totals =	$467.63		$500.8358	$500.85	$500.90	$500.80