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	$79.31	3.487%	$82.0755	$82.08	$82.10	$82.10
Purchase #2	$245.61	13.436%	$278.6102	$278.61	$278.60	$278.60
Purchase #3	$108.31	10.168%	$119.323	$119.32	$119.30	$119.30
Purchase #4	$39.66	11.705%	$44.3022	$44.30	$44.30	$44.30
Purchase #5	$82.68	12.369%	$92.9067	$92.91	$92.90	$92.90
Purchase #6	$116.88	12.383%	$131.3533	$131.35	$131.35	$131.40
Purchase #7	$38.39	5.520%	$40.5091	$40.51	$40.50	$40.50
7 purchase totals =	$710.84		$789.0800	$789.08	$789.05	$789.10