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	$98.59	6.629%	$105.1255	$105.13	$105.15	$105.10
Purchase #2	$160.86	5.807%	$170.2011	$170.20	$170.20	$170.20
Purchase #3	$67.57	13.605%	$76.7629	$76.76	$76.75	$76.80
Purchase #4	$117.47	9.753%	$128.9268	$128.93	$128.95	$128.90
Purchase #5	$133.52	4.751%	$139.8635	$139.86	$139.85	$139.90
Purchase #6	$90.94	4.620%	$95.1414	$95.14	$95.15	$95.10
Purchase #7	$37.69	8.248%	$40.7987	$40.80	$40.80	$40.80
7 purchase totals =	$706.64		$756.8199	$756.82	$756.85	$756.80