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	$229.78	9.583%	$251.7998	$251.80	$251.80	$251.80
Purchase #2	$129.48	12.761%	$146.0029	$146.00	$146.00	$146.00
Purchase #3	$84.42	7.595%	$90.8317	$90.83	$90.85	$90.80
Purchase #4	$52.82	12.479%	$59.4114	$59.41	$59.40	$59.40
Purchase #5	$124.95	10.757%	$138.3909	$138.39	$138.40	$138.40
Purchase #6	$143.43	10.144%	$157.9795	$157.98	$158.00	$158.00
Purchase #7	$191.49	6.254%	$203.4658	$203.47	$203.45	$203.50
7 purchase totals =	$956.37		$1,047.8820	$1,047.88	$1,047.90	$1,047.90