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	$238.68	6.210%	$253.502	$253.50	$253.50	$253.50
Purchase #2	$107.38	8.119%	$116.0982	$116.10	$116.10	$116.10
Purchase #3	$215.79	5.455%	$227.5613	$227.56	$227.55	$227.60
Purchase #4	$92.36	8.636%	$100.3362	$100.34	$100.35	$100.30
Purchase #5	$145.29	8.488%	$157.6222	$157.62	$157.60	$157.60
Purchase #6	$51.77	7.825%	$55.821	$55.82	$55.80	$55.80
Purchase #7	$60.82	10.701%	$67.3283	$67.33	$67.35	$67.30
7 purchase totals =	$912.09		$978.2692	$978.27	$978.25	$978.20