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	$63.38	13.474%	$71.9198	$71.92	$71.90	$71.90
Purchase #2	$114.78	13.418%	$130.1812	$130.18	$130.20	$130.20
Purchase #3	$115.31	13.719%	$131.1294	$131.13	$131.15	$131.10
Purchase #4	$133.55	13.144%	$151.1038	$151.10	$151.10	$151.10
Purchase #5	$116.61	8.344%	$126.3399	$126.34	$126.35	$126.30
Purchase #6	$229.35	7.303%	$246.0994	$246.10	$246.10	$246.10
Purchase #7	$29.50	10.696%	$32.6553	$32.66	$32.65	$32.70
7 purchase totals =	$802.48		$889.4288	$889.43	$889.45	$889.40