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	$179.28	11.787%	$200.4117	$200.41	$200.40	$200.40
Purchase #2	$132.82	13.403%	$150.6219	$150.62	$150.60	$150.60
Purchase #3	$28.94	13.417%	$32.8229	$32.82	$32.80	$32.80
Purchase #4	$30.56	8.647%	$33.2025	$33.20	$33.20	$33.20
Purchase #5	$139.96	7.385%	$150.296	$150.30	$150.30	$150.30
Purchase #6	$50.88	10.855%	$56.403	$56.40	$56.40	$56.40
Purchase #7	$54.49	3.187%	$56.2266	$56.23	$56.25	$56.20
7 purchase totals =	$616.93		$679.9846	$679.98	$679.95	$679.90