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	$46.37	13.200%	$52.4908	$52.49	$52.50	$52.50
Purchase #2	$188.99	13.137%	$213.8176	$213.82	$213.80	$213.80
Purchase #3	$40.82	11.696%	$45.5943	$45.59	$45.60	$45.60
Purchase #4	$84.30	7.420%	$90.5551	$90.56	$90.55	$90.60
Purchase #5	$115.62	4.567%	$120.9004	$120.90	$120.90	$120.90
Purchase #6	$46.70	4.296%	$48.7062	$48.71	$48.70	$48.70
Purchase #7	$224.50	12.444%	$252.4368	$252.44	$252.45	$252.40
7 purchase totals =	$747.30		$824.5012	$824.51	$824.50	$824.50