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	$107.69	9.314%	$117.7202	$117.72	$117.70	$117.70
Purchase #2	$103.96	9.148%	$113.4703	$113.47	$113.45	$113.50
Purchase #3	$60.90	7.706%	$65.593	$65.59	$65.60	$65.60
Purchase #4	$11.47	3.662%	$11.89	$11.89	$11.90	$11.90
Purchase #5	$31.44	4.450%	$32.8391	$32.84	$32.85	$32.80
Purchase #6	$234.32	11.280%	$260.7513	$260.75	$260.75	$260.80
Purchase #7	$123.38	11.401%	$137.4466	$137.45	$137.45	$137.40
7 purchase totals =	$673.16		$739.7105	$739.71	$739.70	$739.70