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	$100.76	10.496%	$111.3358	$111.34	$111.35	$111.30
Purchase #2	$72.57	7.802%	$78.2319	$78.23	$78.25	$78.20
Purchase #3	$58.31	13.715%	$66.3072	$66.31	$66.30	$66.30
Purchase #4	$16.80	13.440%	$19.0579	$19.06	$19.05	$19.10
Purchase #5	$201.60	9.243%	$220.2339	$220.23	$220.25	$220.20
Purchase #6	$207.84	9.446%	$227.4726	$227.47	$227.45	$227.50
Purchase #7	$88.58	5.368%	$93.335	$93.34	$93.35	$93.30
7 purchase totals =	$746.46		$815.9743	$815.98	$816.00	$815.90