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	$189.38	12.446%	$212.9502	$212.95	$212.95	$213.00
Purchase #2	$33.82	11.320%	$37.6484	$37.65	$37.65	$37.60
Purchase #3	$84.81	6.440%	$90.2718	$90.27	$90.25	$90.30
Purchase #4	$218.42	11.621%	$243.8026	$243.80	$243.80	$243.80
Purchase #5	$166.84	3.256%	$172.2723	$172.27	$172.25	$172.30
Purchase #6	$91.63	9.540%	$100.3715	$100.37	$100.35	$100.40
Purchase #7	$27.38	4.503%	$28.6129	$28.61	$28.60	$28.60
7 purchase totals =	$812.28		$885.9297	$885.92	$885.85	$886.00