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	$57.29	13.606%	$65.0849	$65.08	$65.10	$65.10
Purchase #2	$240.52	5.529%	$253.8184	$253.82	$253.80	$253.80
Purchase #3	$11.43	12.406%	$12.848	$12.85	$12.85	$12.80
Purchase #4	$117.73	4.782%	$123.3598	$123.36	$123.35	$123.40
Purchase #5	$177.89	12.752%	$200.5745	$200.57	$200.55	$200.60
Purchase #6	$237.94	11.697%	$265.7718	$265.77	$265.75	$265.80
Purchase #7	$50.61	13.284%	$57.333	$57.33	$57.35	$57.30
7 purchase totals =	$893.41		$978.7904	$978.78	$978.75	$978.80