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	$150.85	12.509%	$169.7198	$169.72	$169.70	$169.70
Purchase #2	$22.77	5.217%	$23.9579	$23.96	$23.95	$24.00
Purchase #3	$59.34	13.360%	$67.2678	$67.27	$67.25	$67.30
Purchase #4	$93.45	11.736%	$104.4173	$104.42	$104.40	$104.40
Purchase #5	$105.69	7.760%	$113.8915	$113.89	$113.90	$113.90
Purchase #6	$127.32	10.569%	$140.7765	$140.78	$140.80	$140.80
Purchase #7	$210.41	13.491%	$238.7964	$238.80	$238.80	$238.80
7 purchase totals =	$769.83		$858.8272	$858.84	$858.80	$858.90