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	$154.68	7.573%	$166.3939	$166.39	$166.40	$166.40
Purchase #2	$85.53	4.380%	$89.2762	$89.28	$89.30	$89.30
Purchase #3	$57.65	12.646%	$64.9404	$64.94	$64.95	$64.90
Purchase #4	$34.29	4.466%	$35.8214	$35.82	$35.80	$35.80
Purchase #5	$211.45	8.477%	$229.3746	$229.37	$229.35	$229.40
Purchase #6	$58.67	12.281%	$65.8753	$65.88	$65.90	$65.90
Purchase #7	$236.53	13.257%	$267.8868	$267.89	$267.90	$267.90
7 purchase totals =	$838.80		$919.5686	$919.57	$919.60	$919.60