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	$128.33	13.688%	$145.8958	$145.90	$145.90	$145.90
Purchase #2	$71.81	13.631%	$81.5984	$81.60	$81.60	$81.60
Purchase #3	$107.51	8.745%	$116.9117	$116.91	$116.90	$116.90
Purchase #4	$243.77	10.127%	$268.4566	$268.46	$268.45	$268.50
Purchase #5	$128.59	3.120%	$132.602	$132.60	$132.60	$132.60
Purchase #6	$48.57	3.349%	$50.1966	$50.20	$50.20	$50.20
Purchase #7	$104.29	3.834%	$108.2885	$108.29	$108.30	$108.30
7 purchase totals =	$832.87		$903.9496	$903.96	$903.95	$904.00