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	$250.64	5.282%	$263.8788	$263.88	$263.90	$263.90
Purchase #2	$241.88	6.448%	$257.4764	$257.48	$257.50	$257.50
Purchase #3	$50.58	6.174%	$53.7028	$53.70	$53.70	$53.70
Purchase #4	$193.61	12.848%	$218.485	$218.49	$218.50	$218.50
Purchase #5	$114.94	10.784%	$127.3351	$127.34	$127.35	$127.30
Purchase #6	$75.95	13.357%	$86.0946	$86.09	$86.10	$86.10
Purchase #7	$72.33	10.481%	$79.9109	$79.91	$79.90	$79.90
7 purchase totals =	$999.93		$1,086.8836	$1,086.89	$1,086.95	$1,086.90