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	$50.65	8.208%	$54.8074	$54.81	$54.80	$54.80
Purchase #2	$44.58	6.156%	$47.3243	$47.32	$47.30	$47.30
Purchase #3	$249.49	7.189%	$267.4258	$267.43	$267.45	$267.40
Purchase #4	$94.78	10.303%	$104.5452	$104.55	$104.55	$104.50
Purchase #5	$11.62	9.516%	$12.7258	$12.73	$12.75	$12.70
Purchase #6	$236.41	13.777%	$268.9802	$268.98	$269.00	$269.00
Purchase #7	$203.78	9.254%	$222.6378	$222.64	$222.65	$222.60
7 purchase totals =	$891.31		$978.4465	$978.46	$978.50	$978.30