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	$229.52	11.643%	$256.243	$256.24	$256.25	$256.20
Purchase #2	$125.54	9.342%	$137.2679	$137.27	$137.25	$137.30
Purchase #3	$58.51	8.134%	$63.2692	$63.27	$63.25	$63.30
Purchase #4	$99.43	4.315%	$103.7204	$103.72	$103.70	$103.70
Purchase #5	$177.25	10.736%	$196.2796	$196.28	$196.30	$196.30
Purchase #6	$36.27	11.783%	$40.5437	$40.54	$40.55	$40.50
Purchase #7	$10.79	11.138%	$11.9918	$11.99	$12.00	$12.00
7 purchase totals =	$737.31		$809.3156	$809.31	$809.30	$809.30