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	$103.67	8.605%	$112.5908	$112.59	$112.60	$112.60
Purchase #2	$128.28	3.427%	$132.6762	$132.68	$132.70	$132.70
Purchase #3	$221.39	7.855%	$238.7802	$238.78	$238.80	$238.80
Purchase #4	$97.28	12.782%	$109.7143	$109.71	$109.70	$109.70
Purchase #5	$43.76	8.369%	$47.4223	$47.42	$47.40	$47.40
Purchase #6	$125.61	12.292%	$141.05	$141.05	$141.05	$141.10
Purchase #7	$119.78	6.532%	$127.604	$127.60	$127.60	$127.60
7 purchase totals =	$839.77		$909.8378	$909.83	$909.85	$909.90