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	$139.64	10.352%	$154.0955	$154.10	$154.10	$154.10
Purchase #2	$69.60	4.152%	$72.4898	$72.49	$72.50	$72.50
Purchase #3	$192.83	4.782%	$202.0511	$202.05	$202.05	$202.10
Purchase #4	$109.62	13.226%	$124.1183	$124.12	$124.10	$124.10
Purchase #5	$29.34	11.736%	$32.7833	$32.78	$32.80	$32.80
Purchase #6	$102.47	13.301%	$116.0995	$116.10	$116.10	$116.10
Purchase #7	$160.74	4.792%	$168.4427	$168.44	$168.45	$168.40
7 purchase totals =	$804.24		$870.0802	$870.08	$870.10	$870.10