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	$78.89	13.291%	$89.3753	$89.38	$89.40	$89.40
Purchase #2	$132.25	7.409%	$142.0484	$142.05	$142.05	$142.00
Purchase #3	$79.60	7.801%	$85.8096	$85.81	$85.80	$85.80
Purchase #4	$26.46	5.769%	$27.9865	$27.99	$28.00	$28.00
Purchase #5	$49.47	3.799%	$51.3494	$51.35	$51.35	$51.30
Purchase #6	$42.79	13.570%	$48.5966	$48.60	$48.60	$48.60
Purchase #7	$219.82	4.334%	$229.347	$229.35	$229.35	$229.30
7 purchase totals =	$629.28		$674.5128	$674.53	$674.55	$674.40