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	$62.61	12.418%	$70.3849	$70.38	$70.40	$70.40
Purchase #2	$59.70	5.842%	$63.1877	$63.19	$63.20	$63.20
Purchase #3	$80.83	12.436%	$90.882	$90.88	$90.90	$90.90
Purchase #4	$89.92	8.841%	$97.8698	$97.87	$97.85	$97.90
Purchase #5	$97.82	8.312%	$105.9508	$105.95	$105.95	$106.00
Purchase #6	$120.58	5.624%	$127.3614	$127.36	$127.35	$127.40
Purchase #7	$81.58	11.544%	$90.9976	$91.00	$91.00	$91.00
7 purchase totals =	$593.04		$646.6342	$646.63	$646.65	$646.80