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	$154.86	8.566%	$168.1253	$168.13	$168.15	$168.10
Purchase #2	$73.69	9.326%	$80.5623	$80.56	$80.55	$80.60
Purchase #3	$147.56	6.628%	$157.3403	$157.34	$157.35	$157.30
Purchase #4	$92.33	13.629%	$104.9137	$104.91	$104.90	$104.90
Purchase #5	$222.83	10.338%	$245.8662	$245.87	$245.85	$245.90
Purchase #6	$26.35	5.524%	$27.8056	$27.81	$27.80	$27.80
Purchase #7	$106.47	9.837%	$116.9435	$116.94	$116.95	$116.90
7 purchase totals =	$824.09		$901.5569	$901.56	$901.55	$901.50