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	$77.68	3.809%	$80.6388	$80.64	$80.65	$80.60
Purchase #2	$166.96	10.108%	$183.8363	$183.84	$183.85	$183.80
Purchase #3	$184.60	6.549%	$196.6895	$196.69	$196.70	$196.70
Purchase #4	$45.86	9.239%	$50.097	$50.10	$50.10	$50.10
Purchase #5	$94.77	4.749%	$99.2706	$99.27	$99.25	$99.30
Purchase #6	$128.27	8.659%	$139.3769	$139.38	$139.40	$139.40
Purchase #7	$215.82	5.325%	$227.3124	$227.31	$227.30	$227.30
7 purchase totals =	$913.96		$977.2215	$977.23	$977.25	$977.20