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	$206.73	10.818%	$229.0941	$229.09	$229.10	$229.10
Purchase #2	$95.86	13.817%	$109.105	$109.11	$109.10	$109.10
Purchase #3	$98.49	6.454%	$104.8465	$104.85	$104.85	$104.80
Purchase #4	$238.56	12.103%	$267.4329	$267.43	$267.45	$267.40
Purchase #5	$12.64	6.766%	$13.4952	$13.50	$13.50	$13.50
Purchase #6	$78.39	4.252%	$81.7231	$81.72	$81.70	$81.70
Purchase #7	$72.43	10.850%	$80.2887	$80.29	$80.30	$80.30
7 purchase totals =	$803.10		$885.9855	$885.99	$886.00	$885.90