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	$123.83	4.564%	$129.4816	$129.48	$129.50	$129.50
Purchase #2	$179.81	8.751%	$195.5452	$195.55	$195.55	$195.50
Purchase #3	$150.63	13.768%	$171.3687	$171.37	$171.35	$171.40
Purchase #4	$100.60	3.795%	$104.4178	$104.42	$104.40	$104.40
Purchase #5	$91.48	11.823%	$102.2957	$102.30	$102.30	$102.30
Purchase #6	$246.89	3.526%	$255.5953	$255.60	$255.60	$255.60
Purchase #7	$115.29	7.355%	$123.7696	$123.77	$123.75	$123.80
7 purchase totals =	$1,008.53		$1,082.4739	$1,082.49	$1,082.45	$1,082.50