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	$51.55	9.283%	$56.3354	$56.34	$56.35	$56.30
Purchase #2	$13.75	13.160%	$15.5595	$15.56	$15.55	$15.60
Purchase #3	$208.39	12.234%	$233.8844	$233.88	$233.90	$233.90
Purchase #4	$208.81	12.171%	$234.2243	$234.22	$234.20	$234.20
Purchase #5	$49.43	5.768%	$52.2811	$52.28	$52.30	$52.30
Purchase #6	$27.98	5.839%	$29.6138	$29.61	$29.60	$29.60
Purchase #7	$129.46	10.364%	$142.8772	$142.88	$142.90	$142.90
7 purchase totals =	$689.37		$764.7757	$764.77	$764.80	$764.80