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	$55.67	7.150%	$59.6504	$59.65	$59.65	$59.70
Purchase #2	$26.68	9.871%	$29.3136	$29.31	$29.30	$29.30
Purchase #3	$117.77	5.534%	$124.2874	$124.29	$124.30	$124.30
Purchase #4	$150.89	3.622%	$156.3552	$156.36	$156.35	$156.40
Purchase #5	$198.60	8.256%	$214.9964	$215.00	$215.00	$215.00
Purchase #6	$178.86	3.222%	$184.6229	$184.62	$184.60	$184.60
Purchase #7	$60.80	9.541%	$66.6009	$66.60	$66.60	$66.60
7 purchase totals =	$789.27		$835.8268	$835.83	$835.80	$835.90