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	$99.62	10.112%	$109.6936	$109.69	$109.70	$109.70
Purchase #2	$40.92	11.432%	$45.598	$45.60	$45.60	$45.60
Purchase #3	$123.28	5.539%	$130.1085	$130.11	$130.10	$130.10
Purchase #4	$168.75	11.813%	$188.6844	$188.68	$188.70	$188.70
Purchase #5	$83.66	11.661%	$93.4156	$93.42	$93.40	$93.40
Purchase #6	$12.35	7.541%	$13.2813	$13.28	$13.30	$13.30
Purchase #7	$85.98	4.652%	$89.9798	$89.98	$90.00	$90.00
7 purchase totals =	$614.56		$670.7612	$670.76	$670.80	$670.80