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	$211.89	11.237%	$235.7001	$235.70	$235.70	$235.70
Purchase #2	$212.66	13.113%	$240.5461	$240.55	$240.55	$240.50
Purchase #3	$123.56	11.115%	$137.2937	$137.29	$137.30	$137.30
Purchase #4	$150.25	12.208%	$168.5925	$168.59	$168.60	$168.60
Purchase #5	$234.50	6.347%	$249.3837	$249.38	$249.40	$249.40
Purchase #6	$51.68	10.314%	$57.0103	$57.01	$57.00	$57.00
Purchase #7	$85.42	8.695%	$92.8473	$92.85	$92.85	$92.80
7 purchase totals =	$1,069.96		$1,181.3737	$1,181.37	$1,181.40	$1,181.30