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	$72.34	8.447%	$78.4506	$78.45	$78.45	$78.50
Purchase #2	$169.59	9.217%	$185.2211	$185.22	$185.20	$185.20
Purchase #3	$249.97	9.794%	$274.4521	$274.45	$274.45	$274.50
Purchase #4	$12.68	6.269%	$13.4749	$13.47	$13.45	$13.50
Purchase #5	$173.37	12.314%	$194.7188	$194.72	$194.70	$194.70
Purchase #6	$224.43	7.819%	$241.9782	$241.98	$242.00	$242.00
Purchase #7	$143.33	4.793%	$150.1998	$150.20	$150.20	$150.20
7 purchase totals =	$1,045.71		$1,138.4955	$1,138.49	$1,138.45	$1,138.60