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	$52.58	12.396%	$59.0978	$59.10	$59.10	$59.10
Purchase #2	$118.26	5.435%	$124.6874	$124.69	$124.70	$124.70
Purchase #3	$249.37	4.444%	$260.452	$260.45	$260.45	$260.50
Purchase #4	$50.52	12.600%	$56.8855	$56.89	$56.90	$56.90
Purchase #5	$135.77	13.344%	$153.8871	$153.89	$153.90	$153.90
Purchase #6	$89.40	7.446%	$96.0567	$96.06	$96.05	$96.10
Purchase #7	$81.47	8.407%	$88.3192	$88.32	$88.30	$88.30
7 purchase totals =	$777.37		$839.3857	$839.40	$839.40	$839.50