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	$199.97	6.275%	$212.5181	$212.52	$212.50	$212.50
Purchase #2	$247.70	12.872%	$279.5839	$279.58	$279.60	$279.60
Purchase #3	$223.77	5.378%	$235.8044	$235.80	$235.80	$235.80
Purchase #4	$90.82	5.539%	$95.8505	$95.85	$95.85	$95.90
Purchase #5	$113.71	5.179%	$119.599	$119.60	$119.60	$119.60
Purchase #6	$88.59	6.433%	$94.289	$94.29	$94.30	$94.30
Purchase #7	$120.80	6.225%	$128.3198	$128.32	$128.30	$128.30
7 purchase totals =	$1,085.36		$1,165.9647	$1,165.96	$1,165.95	$1,166.00