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	$122.53	7.277%	$131.4465	$131.45	$131.45	$131.40
Purchase #2	$140.62	7.835%	$151.6376	$151.64	$151.65	$151.60
Purchase #3	$212.69	3.164%	$219.4195	$219.42	$219.40	$219.40
Purchase #4	$6.92	9.688%	$7.5904	$7.59	$7.60	$7.60
Purchase #5	$229.57	5.242%	$241.6041	$241.60	$241.60	$241.60
Purchase #6	$214.41	12.680%	$241.5972	$241.60	$241.60	$241.60
Purchase #7	$58.58	4.446%	$61.1845	$61.18	$61.20	$61.20
7 purchase totals =	$985.32		$1,054.4798	$1,054.48	$1,054.50	$1,054.40