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	$90.82	10.484%	$100.3416	$100.34	$100.35	$100.30
Purchase #2	$233.57	7.329%	$250.6883	$250.69	$250.70	$250.70
Purchase #3	$150.57	9.241%	$164.4842	$164.48	$164.50	$164.50
Purchase #4	$139.89	5.446%	$147.5084	$147.51	$147.50	$147.50
Purchase #5	$57.81	8.298%	$62.6071	$62.61	$62.60	$62.60
Purchase #6	$138.52	7.224%	$148.5267	$148.53	$148.55	$148.50
Purchase #7	$104.63	8.481%	$113.5037	$113.50	$113.50	$113.50
7 purchase totals =	$915.81		$987.6600	$987.66	$987.70	$987.60