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	$231.55	12.108%	$259.5861	$259.59	$259.60	$259.60
Purchase #2	$42.70	9.346%	$46.6907	$46.69	$46.70	$46.70
Purchase #3	$218.78	9.199%	$238.9056	$238.91	$238.90	$238.90
Purchase #4	$124.87	9.132%	$136.2731	$136.27	$136.25	$136.30
Purchase #5	$63.25	11.375%	$70.4447	$70.44	$70.45	$70.40
Purchase #6	$128.60	11.174%	$142.9698	$142.97	$142.95	$143.00
Purchase #7	$113.62	4.404%	$118.6238	$118.62	$118.60	$118.60
7 purchase totals =	$923.37		$1,013.4938	$1,013.49	$1,013.45	$1,013.50