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	$27.98	6.718%	$29.8597	$29.86	$29.85	$29.90
Purchase #2	$176.29	13.575%	$200.2214	$200.22	$200.20	$200.20
Purchase #3	$179.45	3.527%	$185.7792	$185.78	$185.80	$185.80
Purchase #4	$103.54	6.479%	$110.2484	$110.25	$110.25	$110.20
Purchase #5	$63.88	12.399%	$71.8005	$71.80	$71.80	$71.80
Purchase #6	$217.86	6.105%	$231.1604	$231.16	$231.15	$231.20
Purchase #7	$23.25	11.385%	$25.897	$25.90	$25.90	$25.90
7 purchase totals =	$792.25		$854.9666	$854.97	$854.95	$855.00