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	$60.48	13.848%	$68.8553	$68.86	$68.85	$68.90
Purchase #2	$40.89	8.862%	$44.5137	$44.51	$44.50	$44.50
Purchase #3	$166.95	9.843%	$183.3829	$183.38	$183.40	$183.40
Purchase #4	$231.84	13.804%	$263.8432	$263.84	$263.85	$263.80
Purchase #5	$18.58	12.193%	$20.8455	$20.85	$20.85	$20.80
Purchase #6	$227.59	7.128%	$243.8126	$243.81	$243.80	$243.80
Purchase #7	$59.79	9.684%	$65.5801	$65.58	$65.60	$65.60
7 purchase totals =	$806.12		$890.8333	$890.83	$890.85	$890.80