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	$127.40	13.800%	$144.9812	$144.98	$145.00	$145.00
Purchase #2	$38.95	13.607%	$44.2499	$44.25	$44.25	$44.20
Purchase #3	$54.86	8.429%	$59.4841	$59.48	$59.50	$59.50
Purchase #4	$222.51	9.491%	$243.6284	$243.63	$243.65	$243.60
Purchase #5	$175.64	7.631%	$189.0431	$189.04	$189.05	$189.00
Purchase #6	$74.49	7.393%	$79.997	$80.00	$80.00	$80.00
Purchase #7	$154.95	8.595%	$168.268	$168.27	$168.25	$168.30
7 purchase totals =	$848.80		$929.6517	$929.65	$929.70	$929.60