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	$202.55	4.723%	$212.1164	$212.12	$212.10	$212.10
Purchase #2	$131.89	7.355%	$141.5905	$141.59	$141.60	$141.60
Purchase #3	$152.66	9.307%	$166.8681	$166.87	$166.85	$166.90
Purchase #4	$35.87	5.716%	$37.9203	$37.92	$37.90	$37.90
Purchase #5	$64.80	9.628%	$71.0389	$71.04	$71.05	$71.00
Purchase #6	$50.89	11.639%	$56.8131	$56.81	$56.80	$56.80
Purchase #7	$172.70	3.853%	$179.3541	$179.35	$179.35	$179.40
7 purchase totals =	$811.36		$865.7014	$865.70	$865.65	$865.70