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	$113.45	5.563%	$119.7612	$119.76	$119.75	$119.80
Purchase #2	$157.95	8.436%	$171.2747	$171.27	$171.25	$171.30
Purchase #3	$57.60	6.138%	$61.1355	$61.14	$61.15	$61.10
Purchase #4	$151.31	13.519%	$171.7656	$171.77	$171.75	$171.80
Purchase #5	$85.59	11.472%	$95.4089	$95.41	$95.40	$95.40
Purchase #6	$45.42	8.516%	$49.288	$49.29	$49.30	$49.30
Purchase #7	$234.96	4.378%	$245.2465	$245.25	$245.25	$245.20
7 purchase totals =	$846.28		$913.8804	$913.89	$913.85	$913.90