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	$215.71	9.473%	$236.1442	$236.14	$236.15	$236.10
Purchase #2	$159.76	5.649%	$168.7848	$168.78	$168.80	$168.80
Purchase #3	$176.85	12.463%	$198.8908	$198.89	$198.90	$198.90
Purchase #4	$67.37	6.448%	$71.714	$71.71	$71.70	$71.70
Purchase #5	$77.61	10.290%	$85.5961	$85.60	$85.60	$85.60
Purchase #6	$16.42	12.723%	$18.5091	$18.51	$18.50	$18.50
Purchase #7	$103.33	12.677%	$116.4291	$116.43	$116.45	$116.40
7 purchase totals =	$817.05		$896.0681	$896.06	$896.10	$896.00