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	$80.71	13.443%	$91.5598	$91.56	$91.55	$91.60
Purchase #2	$140.74	5.569%	$148.5778	$148.58	$148.60	$148.60
Purchase #3	$44.69	6.520%	$47.6038	$47.60	$47.60	$47.60
Purchase #4	$46.82	11.831%	$52.3593	$52.36	$52.35	$52.40
Purchase #5	$130.71	6.756%	$139.5408	$139.54	$139.55	$139.50
Purchase #6	$138.92	13.458%	$157.6159	$157.62	$157.60	$157.60
Purchase #7	$25.85	11.762%	$28.8905	$28.89	$28.90	$28.90
7 purchase totals =	$608.44		$666.1479	$666.15	$666.15	$666.20