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	$166.30	12.657%	$187.3486	$187.35	$187.35	$187.30
Purchase #2	$83.49	8.364%	$90.4731	$90.47	$90.45	$90.50
Purchase #3	$111.62	4.206%	$116.3147	$116.31	$116.30	$116.30
Purchase #4	$133.97	12.588%	$150.8341	$150.83	$150.85	$150.80
Purchase #5	$222.61	4.860%	$233.4288	$233.43	$233.45	$233.40
Purchase #6	$61.49	3.773%	$63.81	$63.81	$63.80	$63.80
Purchase #7	$13.90	6.722%	$14.8344	$14.83	$14.85	$14.80
7 purchase totals =	$793.38		$857.0437	$857.03	$857.05	$856.90