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	$234.79	12.395%	$263.8922	$263.89	$263.90	$263.90
Purchase #2	$249.88	3.572%	$258.8057	$258.81	$258.80	$258.80
Purchase #3	$109.54	12.704%	$123.456	$123.46	$123.45	$123.50
Purchase #4	$96.40	12.747%	$108.6881	$108.69	$108.70	$108.70
Purchase #5	$71.78	9.294%	$78.4512	$78.45	$78.45	$78.50
Purchase #6	$85.67	6.653%	$91.3696	$91.37	$91.35	$91.40
Purchase #7	$201.47	6.438%	$214.4406	$214.44	$214.45	$214.40
7 purchase totals =	$1,049.53		$1,139.1034	$1,139.11	$1,139.10	$1,139.20