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	$59.74	4.111%	$62.1959	$62.20	$62.20	$62.20
Purchase #2	$119.44	11.629%	$133.3297	$133.33	$133.35	$133.30
Purchase #3	$106.77	5.593%	$112.7416	$112.74	$112.75	$112.70
Purchase #4	$158.98	13.766%	$180.8652	$180.87	$180.85	$180.90
Purchase #5	$110.58	8.317%	$119.7769	$119.78	$119.80	$119.80
Purchase #6	$80.64	11.860%	$90.2039	$90.20	$90.20	$90.20
Purchase #7	$137.50	3.604%	$142.4555	$142.46	$142.45	$142.50
7 purchase totals =	$773.65		$841.5687	$841.58	$841.60	$841.60