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	$173.78	8.424%	$188.4192	$188.42	$188.40	$188.40
Purchase #2	$132.80	13.608%	$150.8714	$150.87	$150.85	$150.90
Purchase #3	$84.72	6.486%	$90.2149	$90.21	$90.20	$90.20
Purchase #4	$29.52	9.182%	$32.2305	$32.23	$32.25	$32.20
Purchase #5	$175.42	5.365%	$184.8313	$184.83	$184.85	$184.80
Purchase #6	$63.28	4.400%	$66.0643	$66.06	$66.05	$66.10
Purchase #7	$213.38	5.399%	$224.9004	$224.90	$224.90	$224.90
7 purchase totals =	$872.90		$937.5320	$937.52	$937.50	$937.50