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	$81.43	11.737%	$90.9874	$90.99	$91.00	$91.00
Purchase #2	$146.25	13.219%	$165.5828	$165.58	$165.60	$165.60
Purchase #3	$52.59	5.749%	$55.6134	$55.61	$55.60	$55.60
Purchase #4	$54.81	11.861%	$61.311	$61.31	$61.30	$61.30
Purchase #5	$181.65	9.832%	$199.5098	$199.51	$199.50	$199.50
Purchase #6	$244.37	8.791%	$265.8526	$265.85	$265.85	$265.90
Purchase #7	$34.37	3.152%	$35.4533	$35.45	$35.45	$35.50
7 purchase totals =	$795.47		$874.3103	$874.30	$874.30	$874.40