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	$97.87	11.365%	$108.9929	$108.99	$109.00	$109.00
Purchase #2	$175.41	3.698%	$181.8967	$181.90	$181.90	$181.90
Purchase #3	$234.92	13.157%	$265.8284	$265.83	$265.85	$265.80
Purchase #4	$108.73	3.176%	$112.1833	$112.18	$112.20	$112.20
Purchase #5	$21.47	8.658%	$23.3289	$23.33	$23.35	$23.30
Purchase #6	$57.27	3.576%	$59.318	$59.32	$59.30	$59.30
Purchase #7	$134.59	11.637%	$150.2522	$150.25	$150.25	$150.30
7 purchase totals =	$830.26		$901.8004	$901.80	$901.85	$901.80