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	$17.45	10.459%	$19.2751	$19.28	$19.30	$19.30
Purchase #2	$44.55	7.576%	$47.9251	$47.93	$47.95	$47.90
Purchase #3	$221.62	3.671%	$229.7557	$229.76	$229.75	$229.80
Purchase #4	$102.88	11.380%	$114.5877	$114.59	$114.60	$114.60
Purchase #5	$37.95	8.190%	$41.0581	$41.06	$41.05	$41.10
Purchase #6	$56.38	4.812%	$59.093	$59.09	$59.10	$59.10
Purchase #7	$66.96	8.676%	$72.7694	$72.77	$72.75	$72.80
7 purchase totals =	$547.79		$584.4641	$584.48	$584.50	$584.60