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	$74.38	7.333%	$79.8343	$79.83	$79.85	$79.80
Purchase #2	$33.74	12.129%	$37.8323	$37.83	$37.85	$37.80
Purchase #3	$84.49	7.136%	$90.5192	$90.52	$90.50	$90.50
Purchase #4	$6.32	11.695%	$7.0591	$7.06	$7.05	$7.10
Purchase #5	$122.79	9.487%	$134.4391	$134.44	$134.45	$134.40
Purchase #6	$197.76	10.260%	$218.0502	$218.05	$218.05	$218.10
Purchase #7	$104.59	11.502%	$116.6199	$116.62	$116.60	$116.60
7 purchase totals =	$624.07		$684.3541	$684.35	$684.35	$684.30