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	$234.89	5.105%	$246.8811	$246.88	$246.90	$246.90
Purchase #2	$174.26	6.533%	$185.6444	$185.64	$185.65	$185.60
Purchase #3	$86.42	5.159%	$90.8784	$90.88	$90.90	$90.90
Purchase #4	$246.67	9.486%	$270.0691	$270.07	$270.05	$270.10
Purchase #5	$17.80	6.233%	$18.9095	$18.91	$18.90	$18.90
Purchase #6	$10.58	3.107%	$10.9087	$10.91	$10.90	$10.90
Purchase #7	$203.44	8.565%	$220.8646	$220.86	$220.85	$220.90
7 purchase totals =	$974.06		$1,044.1558	$1,044.15	$1,044.15	$1,044.20