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	$20.36	13.686%	$23.1465	$23.15	$23.15	$23.10
Purchase #2	$80.98	9.743%	$88.8699	$88.87	$88.85	$88.90
Purchase #3	$51.88	4.489%	$54.2089	$54.21	$54.20	$54.20
Purchase #4	$53.42	4.323%	$55.7293	$55.73	$55.75	$55.70
Purchase #5	$67.44	6.862%	$72.0677	$72.07	$72.05	$72.10
Purchase #6	$14.98	13.659%	$17.0261	$17.03	$17.05	$17.00
Purchase #7	$179.43	9.537%	$196.5422	$196.54	$196.55	$196.50
7 purchase totals =	$468.49		$507.5906	$507.60	$507.60	$507.50