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	$11.53	13.712%	$13.111	$13.11	$13.10	$13.10
Purchase #2	$243.50	13.766%	$277.0202	$277.02	$277.00	$277.00
Purchase #3	$220.28	3.654%	$228.329	$228.33	$228.35	$228.30
Purchase #4	$220.42	10.230%	$242.969	$242.97	$242.95	$243.00
Purchase #5	$173.83	7.778%	$187.3505	$187.35	$187.35	$187.40
Purchase #6	$31.42	5.154%	$33.0394	$33.04	$33.05	$33.00
Purchase #7	$35.99	3.250%	$37.1597	$37.16	$37.15	$37.20
7 purchase totals =	$936.97		$1,018.9788	$1,018.98	$1,018.95	$1,019.00