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	$177.71	4.606%	$185.8953	$185.90	$185.90	$185.90
Purchase #2	$209.58	6.601%	$223.4144	$223.41	$223.40	$223.40
Purchase #3	$250.33	6.193%	$265.8329	$265.83	$265.85	$265.80
Purchase #4	$43.65	10.315%	$48.1525	$48.15	$48.15	$48.20
Purchase #5	$21.69	12.546%	$24.4112	$24.41	$24.40	$24.40
Purchase #6	$120.98	12.635%	$136.2658	$136.27	$136.25	$136.30
Purchase #7	$123.51	12.681%	$139.1723	$139.17	$139.15	$139.20
7 purchase totals =	$947.45		$1,023.1444	$1,023.14	$1,023.10	$1,023.20