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	$195.96	13.473%	$222.3617	$222.36	$222.35	$222.40
Purchase #2	$72.73	8.566%	$78.9601	$78.96	$78.95	$79.00
Purchase #3	$67.91	3.764%	$70.4661	$70.47	$70.45	$70.50
Purchase #4	$214.81	11.628%	$239.7881	$239.79	$239.80	$239.80
Purchase #5	$29.48	4.190%	$30.7152	$30.72	$30.70	$30.70
Purchase #6	$90.81	10.297%	$100.1607	$100.16	$100.15	$100.20
Purchase #7	$158.89	8.376%	$172.1986	$172.20	$172.20	$172.20
7 purchase totals =	$830.59		$914.6505	$914.66	$914.60	$914.80