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	$14.40	8.408%	$15.6108	$15.61	$15.60	$15.60
Purchase #2	$64.38	3.514%	$66.6423	$66.64	$66.65	$66.60
Purchase #3	$187.30	7.748%	$201.812	$201.81	$201.80	$201.80
Purchase #4	$82.36	9.309%	$90.0269	$90.03	$90.05	$90.00
Purchase #5	$35.40	11.158%	$39.3499	$39.35	$39.35	$39.30
Purchase #6	$54.59	8.768%	$59.3765	$59.38	$59.40	$59.40
Purchase #7	$36.88	13.132%	$41.7231	$41.72	$41.70	$41.70
7 purchase totals =	$475.31		$514.5415	$514.54	$514.55	$514.40