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	$248.52	13.689%	$282.5399	$282.54	$282.55	$282.50
Purchase #2	$92.66	8.344%	$100.3916	$100.39	$100.40	$100.40
Purchase #3	$124.60	3.285%	$128.6931	$128.69	$128.70	$128.70
Purchase #4	$65.80	6.845%	$70.304	$70.30	$70.30	$70.30
Purchase #5	$86.32	9.792%	$94.7725	$94.77	$94.75	$94.80
Purchase #6	$8.89	6.538%	$9.4712	$9.47	$9.45	$9.50
Purchase #7	$199.71	9.300%	$218.283	$218.28	$218.30	$218.30
7 purchase totals =	$826.50		$904.4553	$904.44	$904.45	$904.50