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	$91.29	9.360%	$99.8347	$99.83	$99.85	$99.80
Purchase #2	$95.91	6.711%	$102.3465	$102.35	$102.35	$102.30
Purchase #3	$10.63	13.210%	$12.0342	$12.03	$12.05	$12.00
Purchase #4	$75.63	13.432%	$85.7886	$85.79	$85.80	$85.80
Purchase #5	$96.50	9.365%	$105.5372	$105.54	$105.55	$105.50
Purchase #6	$143.42	3.773%	$148.8312	$148.83	$148.85	$148.80
Purchase #7	$173.77	10.615%	$192.2157	$192.22	$192.20	$192.20
7 purchase totals =	$687.15		$746.5881	$746.59	$746.65	$746.40