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	$9.59	9.190%	$10.4713	$10.47	$10.45	$10.50
Purchase #2	$219.28	11.325%	$244.1135	$244.11	$244.10	$244.10
Purchase #3	$81.53	10.286%	$89.9162	$89.92	$89.90	$89.90
Purchase #4	$97.59	9.675%	$107.0318	$107.03	$107.05	$107.00
Purchase #5	$9.97	6.409%	$10.609	$10.61	$10.60	$10.60
Purchase #6	$54.95	12.591%	$61.8688	$61.87	$61.85	$61.90
Purchase #7	$35.88	11.112%	$39.867	$39.87	$39.85	$39.90
7 purchase totals =	$508.79		$563.8776	$563.88	$563.80	$563.90