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	$44.47	12.123%	$49.8611	$49.86	$49.85	$49.90
Purchase #2	$52.81	13.339%	$59.8543	$59.85	$59.85	$59.90
Purchase #3	$14.61	11.628%	$16.3089	$16.31	$16.30	$16.30
Purchase #4	$96.46	6.269%	$102.5071	$102.51	$102.50	$102.50
Purchase #5	$39.79	10.318%	$43.8955	$43.90	$43.90	$43.90
Purchase #6	$247.39	3.795%	$256.7785	$256.78	$256.80	$256.80
Purchase #7	$58.95	7.798%	$63.5469	$63.55	$63.55	$63.50
7 purchase totals =	$554.48		$592.7523	$592.76	$592.75	$592.80