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	$81.36	9.800%	$89.3333	$89.33	$89.35	$89.30
Purchase #2	$100.38	4.411%	$104.8078	$104.81	$104.80	$104.80
Purchase #3	$103.97	12.495%	$116.9611	$116.96	$116.95	$117.00
Purchase #4	$146.36	11.113%	$162.625	$162.63	$162.65	$162.60
Purchase #5	$48.97	11.559%	$54.6304	$54.63	$54.65	$54.60
Purchase #6	$76.77	8.824%	$83.5442	$83.54	$83.55	$83.50
Purchase #7	$118.70	6.517%	$126.4357	$126.44	$126.45	$126.40
7 purchase totals =	$676.51		$738.3375	$738.34	$738.40	$738.20