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	$101.67	6.265%	$108.0396	$108.04	$108.05	$108.00
Purchase #2	$82.46	9.337%	$90.1593	$90.16	$90.15	$90.20
Purchase #3	$57.89	4.357%	$60.4123	$60.41	$60.40	$60.40
Purchase #4	$237.95	10.417%	$262.7373	$262.74	$262.75	$262.70
Purchase #5	$160.47	11.389%	$178.7459	$178.75	$178.75	$178.70
Purchase #6	$59.59	13.520%	$67.6466	$67.65	$67.65	$67.60
Purchase #7	$42.34	10.682%	$46.8628	$46.86	$46.85	$46.90
7 purchase totals =	$742.37		$814.6038	$814.61	$814.60	$814.50