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	$215.81	6.305%	$229.4168	$229.42	$229.40	$229.40
Purchase #2	$38.71	9.397%	$42.3476	$42.35	$42.35	$42.30
Purchase #3	$11.96	7.292%	$12.8321	$12.83	$12.85	$12.80
Purchase #4	$63.98	4.486%	$66.8501	$66.85	$66.85	$66.90
Purchase #5	$95.38	7.464%	$102.4992	$102.50	$102.50	$102.50
Purchase #6	$239.66	6.173%	$254.4542	$254.45	$254.45	$254.50
Purchase #7	$168.71	9.791%	$185.2284	$185.23	$185.25	$185.20
7 purchase totals =	$834.21		$893.6284	$893.63	$893.65	$893.60