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	$203.46	10.424%	$224.6687	$224.67	$224.65	$224.70
Purchase #2	$220.62	5.109%	$231.8915	$231.89	$231.90	$231.90
Purchase #3	$72.38	9.113%	$78.976	$78.98	$79.00	$79.00
Purchase #4	$119.98	11.530%	$133.8137	$133.81	$133.80	$133.80
Purchase #5	$216.79	12.510%	$243.9104	$243.91	$243.90	$243.90
Purchase #6	$51.54	6.208%	$54.7396	$54.74	$54.75	$54.70
Purchase #7	$127.50	3.705%	$132.2239	$132.22	$132.20	$132.20
7 purchase totals =	$1,012.27		$1,100.2238	$1,100.22	$1,100.20	$1,100.20