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	$203.50	10.788%	$225.4536	$225.45	$225.45	$225.50
Purchase #2	$147.89	5.265%	$155.6764	$155.68	$155.70	$155.70
Purchase #3	$148.92	3.633%	$154.3303	$154.33	$154.35	$154.30
Purchase #4	$151.26	11.124%	$168.0862	$168.09	$168.10	$168.10
Purchase #5	$200.38	13.416%	$227.263	$227.26	$227.25	$227.30
Purchase #6	$220.30	8.465%	$238.9484	$238.95	$238.95	$238.90
Purchase #7	$125.27	4.609%	$131.0437	$131.04	$131.05	$131.00
7 purchase totals =	$1,197.52		$1,300.8016	$1,300.80	$1,300.85	$1,300.80