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	$113.66	9.545%	$124.5088	$124.51	$124.50	$124.50
Purchase #2	$75.38	3.386%	$77.9324	$77.93	$77.95	$77.90
Purchase #3	$16.60	10.604%	$18.3603	$18.36	$18.35	$18.40
Purchase #4	$179.48	6.724%	$191.5482	$191.55	$191.55	$191.50
Purchase #5	$105.53	6.453%	$112.3399	$112.34	$112.35	$112.30
Purchase #6	$83.28	6.229%	$88.4675	$88.47	$88.45	$88.50
Purchase #7	$31.34	5.495%	$33.0621	$33.06	$33.05	$33.10
7 purchase totals =	$605.27		$646.2192	$646.22	$646.20	$646.20