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	$170.72	11.131%	$189.7228	$189.72	$189.70	$189.70
Purchase #2	$132.61	4.174%	$138.1451	$138.15	$138.15	$138.10
Purchase #3	$106.97	10.420%	$118.1163	$118.12	$118.10	$118.10
Purchase #4	$39.48	8.674%	$42.9045	$42.90	$42.90	$42.90
Purchase #5	$6.83	8.338%	$7.3995	$7.40	$7.40	$7.40
Purchase #6	$248.67	7.782%	$268.0215	$268.02	$268.00	$268.00
Purchase #7	$106.32	11.545%	$118.5946	$118.59	$118.60	$118.60
7 purchase totals =	$811.60		$882.9043	$882.90	$882.85	$882.80