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	$150.60	4.834%	$157.88	$157.88	$157.90	$157.90
Purchase #2	$35.49	8.436%	$38.4839	$38.48	$38.50	$38.50
Purchase #3	$44.63	8.365%	$48.3633	$48.36	$48.35	$48.40
Purchase #4	$102.86	4.385%	$107.3704	$107.37	$107.35	$107.40
Purchase #5	$49.32	8.109%	$53.3194	$53.32	$53.30	$53.30
Purchase #6	$35.66	4.506%	$37.2668	$37.27	$37.25	$37.30
Purchase #7	$59.89	13.847%	$68.183	$68.18	$68.20	$68.20
7 purchase totals =	$478.45		$510.8668	$510.86	$510.85	$511.00