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	$242.49	11.854%	$271.2348	$271.23	$271.25	$271.20
Purchase #2	$75.78	3.267%	$78.2557	$78.26	$78.25	$78.30
Purchase #3	$56.25	9.443%	$61.5617	$61.56	$61.55	$61.60
Purchase #4	$53.93	11.844%	$60.3175	$60.32	$60.30	$60.30
Purchase #5	$103.87	8.794%	$113.0043	$113.00	$113.00	$113.00
Purchase #6	$99.33	5.419%	$104.7127	$104.71	$104.70	$104.70
Purchase #7	$53.59	11.219%	$59.6023	$59.60	$59.60	$59.60
7 purchase totals =	$685.24		$748.6890	$748.68	$748.65	$748.70