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	$112.45	13.695%	$127.85	$127.85	$127.85	$127.90
Purchase #2	$190.33	11.848%	$212.8803	$212.88	$212.90	$212.90
Purchase #3	$151.72	3.355%	$156.8102	$156.81	$156.80	$156.80
Purchase #4	$103.57	10.316%	$114.2543	$114.25	$114.25	$114.30
Purchase #5	$250.38	12.540%	$281.7777	$281.78	$281.80	$281.80
Purchase #6	$122.86	7.111%	$131.5966	$131.60	$131.60	$131.60
Purchase #7	$49.74	9.538%	$54.4842	$54.48	$54.50	$54.50
7 purchase totals =	$981.05		$1,079.6533	$1,079.65	$1,079.70	$1,079.80