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	$241.74	13.583%	$274.5755	$274.58	$274.60	$274.60
Purchase #2	$83.97	7.308%	$90.1065	$90.11	$90.10	$90.10
Purchase #3	$89.25	13.580%	$101.3702	$101.37	$101.35	$101.40
Purchase #4	$163.83	6.624%	$174.6821	$174.68	$174.70	$174.70
Purchase #5	$77.43	8.314%	$83.8675	$83.87	$83.85	$83.90
Purchase #6	$25.79	9.246%	$28.1745	$28.17	$28.15	$28.20
Purchase #7	$108.63	13.595%	$123.3982	$123.40	$123.40	$123.40
7 purchase totals =	$790.64		$876.1745	$876.18	$876.15	$876.30