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	$15.83	4.353%	$16.5191	$16.52	$16.50	$16.50
Purchase #2	$72.54	11.653%	$80.9931	$80.99	$81.00	$81.00
Purchase #3	$99.63	5.825%	$105.4334	$105.43	$105.45	$105.40
Purchase #4	$143.95	5.229%	$151.4771	$151.48	$151.50	$151.50
Purchase #5	$71.90	9.658%	$78.8441	$78.84	$78.85	$78.80
Purchase #6	$85.35	10.586%	$94.3852	$94.39	$94.40	$94.40
Purchase #7	$205.86	9.652%	$225.7296	$225.73	$225.75	$225.70
7 purchase totals =	$695.06		$753.3816	$753.38	$753.45	$753.30