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	$30.51	6.441%	$32.4751	$32.48	$32.50	$32.50
Purchase #2	$92.92	13.422%	$105.3917	$105.39	$105.40	$105.40
Purchase #3	$118.50	4.544%	$123.8846	$123.88	$123.90	$123.90
Purchase #4	$37.45	11.616%	$41.8002	$41.80	$41.80	$41.80
Purchase #5	$179.38	10.359%	$197.962	$197.96	$197.95	$198.00
Purchase #6	$249.82	9.112%	$272.5836	$272.58	$272.60	$272.60
Purchase #7	$136.78	8.123%	$147.8906	$147.89	$147.90	$147.90
7 purchase totals =	$845.36		$921.9878	$921.98	$922.05	$922.10