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	$156.58	10.134%	$172.4478	$172.45	$172.45	$172.40
Purchase #2	$86.27	4.283%	$89.9649	$89.96	$89.95	$90.00
Purchase #3	$104.41	12.517%	$117.479	$117.48	$117.50	$117.50
Purchase #4	$224.25	3.243%	$231.5224	$231.52	$231.50	$231.50
Purchase #5	$208.29	9.657%	$228.4046	$228.40	$228.40	$228.40
Purchase #6	$90.54	6.862%	$96.7529	$96.75	$96.75	$96.80
Purchase #7	$50.37	5.812%	$53.2975	$53.30	$53.30	$53.30
7 purchase totals =	$920.71		$989.8691	$989.86	$989.85	$989.90