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	$155.48	10.186%	$171.3172	$171.32	$171.30	$171.30
Purchase #2	$56.72	7.316%	$60.8696	$60.87	$60.85	$60.90
Purchase #3	$148.45	13.580%	$168.6095	$168.61	$168.60	$168.60
Purchase #4	$117.25	12.314%	$131.6882	$131.69	$131.70	$131.70
Purchase #5	$239.32	8.105%	$258.7169	$258.72	$258.70	$258.70
Purchase #6	$73.97	8.145%	$79.9949	$79.99	$80.00	$80.00
Purchase #7	$157.59	3.148%	$162.5509	$162.55	$162.55	$162.60
7 purchase totals =	$948.78		$1,033.7472	$1,033.75	$1,033.70	$1,033.80