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	$163.64	9.530%	$179.2349	$179.23	$179.25	$179.20
Purchase #2	$174.63	10.269%	$192.5628	$192.56	$192.55	$192.60
Purchase #3	$208.82	12.317%	$234.5404	$234.54	$234.55	$234.50
Purchase #4	$154.36	5.126%	$162.2725	$162.27	$162.25	$162.30
Purchase #5	$191.25	4.322%	$199.5158	$199.52	$199.50	$199.50
Purchase #6	$123.85	10.472%	$136.8196	$136.82	$136.80	$136.80
Purchase #7	$131.39	4.274%	$137.0056	$137.01	$137.00	$137.00
7 purchase totals =	$1,147.94		$1,241.9516	$1,241.95	$1,241.90	$1,241.90