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	$244.69	10.500%	$270.3825	$270.38	$270.40	$270.40
Purchase #2	$56.90	13.170%	$64.3937	$64.39	$64.40	$64.40
Purchase #3	$133.33	9.527%	$146.0323	$146.03	$146.05	$146.00
Purchase #4	$176.31	3.108%	$181.7897	$181.79	$181.80	$181.80
Purchase #5	$96.88	8.136%	$104.7622	$104.76	$104.75	$104.80
Purchase #6	$179.60	10.404%	$198.2856	$198.29	$198.30	$198.30
Purchase #7	$135.54	7.771%	$146.0728	$146.07	$146.05	$146.10
7 purchase totals =	$1,023.25		$1,111.7188	$1,111.71	$1,111.75	$1,111.80