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	$171.63	4.404%	$179.1886	$179.19	$179.20	$179.20
Purchase #2	$146.73	3.316%	$151.5956	$151.60	$151.60	$151.60
Purchase #3	$118.27	4.598%	$123.7081	$123.71	$123.70	$123.70
Purchase #4	$80.75	11.455%	$89.9999	$90.00	$90.00	$90.00
Purchase #5	$222.78	12.326%	$250.2399	$250.24	$250.25	$250.20
Purchase #6	$110.45	7.686%	$118.9392	$118.94	$118.95	$118.90
Purchase #7	$166.95	5.567%	$176.2441	$176.24	$176.25	$176.20
7 purchase totals =	$1,017.56		$1,089.9154	$1,089.92	$1,089.95	$1,089.80