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	$28.74	9.127%	$31.3631	$31.36	$31.35	$31.40
Purchase #2	$58.67	13.220%	$66.4262	$66.43	$66.45	$66.40
Purchase #3	$86.51	6.854%	$92.4394	$92.44	$92.45	$92.40
Purchase #4	$100.53	4.684%	$105.2388	$105.24	$105.25	$105.20
Purchase #5	$22.84	10.686%	$25.2807	$25.28	$25.30	$25.30
Purchase #6	$148.47	12.242%	$166.6457	$166.65	$166.65	$166.60
Purchase #7	$182.67	4.270%	$190.47	$190.47	$190.45	$190.50
7 purchase totals =	$628.43		$677.8639	$677.87	$677.90	$677.80