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	$188.31	10.339%	$207.7794	$207.78	$207.80	$207.80
Purchase #2	$234.33	10.209%	$258.2527	$258.25	$258.25	$258.30
Purchase #3	$59.97	11.753%	$67.0183	$67.02	$67.00	$67.00
Purchase #4	$68.87	4.739%	$72.1337	$72.13	$72.15	$72.10
Purchase #5	$62.41	4.797%	$65.4038	$65.40	$65.40	$65.40
Purchase #6	$95.95	5.749%	$101.4662	$101.47	$101.45	$101.50
Purchase #7	$39.62	8.399%	$42.9477	$42.95	$42.95	$42.90
7 purchase totals =	$749.46		$815.0018	$815.00	$815.00	$815.00