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	$173.33	3.511%	$179.4156	$179.42	$179.40	$179.40
Purchase #2	$21.33	12.110%	$23.9131	$23.91	$23.90	$23.90
Purchase #3	$141.70	3.456%	$146.5972	$146.60	$146.60	$146.60
Purchase #4	$152.35	9.552%	$166.9025	$166.90	$166.90	$166.90
Purchase #5	$159.80	7.528%	$171.8297	$171.83	$171.85	$171.80
Purchase #6	$186.80	7.116%	$200.0927	$200.09	$200.10	$200.10
Purchase #7	$76.36	13.739%	$86.8511	$86.85	$86.85	$86.90
7 purchase totals =	$911.67		$975.6019	$975.60	$975.60	$975.60