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	$234.84	9.741%	$257.7158	$257.72	$257.70	$257.70
Purchase #2	$180.90	13.374%	$205.0936	$205.09	$205.10	$205.10
Purchase #3	$35.71	13.313%	$40.4641	$40.46	$40.45	$40.50
Purchase #4	$69.84	4.430%	$72.9339	$72.93	$72.95	$72.90
Purchase #5	$115.89	6.572%	$123.5063	$123.51	$123.50	$123.50
Purchase #6	$175.66	7.726%	$189.2315	$189.23	$189.25	$189.20
Purchase #7	$130.72	13.162%	$147.9254	$147.93	$147.95	$147.90
7 purchase totals =	$943.56		$1,036.8706	$1,036.87	$1,036.90	$1,036.80