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	$82.48	9.765%	$90.5342	$90.53	$90.55	$90.50
Purchase #2	$233.53	10.436%	$257.9012	$257.90	$257.90	$257.90
Purchase #3	$18.97	8.124%	$20.5111	$20.51	$20.50	$20.50
Purchase #4	$241.90	11.836%	$270.5313	$270.53	$270.55	$270.50
Purchase #5	$30.88	5.578%	$32.6025	$32.60	$32.60	$32.60
Purchase #6	$175.63	13.743%	$199.7668	$199.77	$199.75	$199.80
Purchase #7	$34.79	5.846%	$36.8238	$36.82	$36.80	$36.80
7 purchase totals =	$818.18		$908.6709	$908.66	$908.65	$908.60