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	$39.39	6.732%	$42.0417	$42.04	$42.05	$42.00
Purchase #2	$77.75	11.295%	$86.5319	$86.53	$86.55	$86.50
Purchase #3	$78.68	13.305%	$89.1484	$89.15	$89.15	$89.10
Purchase #4	$141.60	11.314%	$157.6206	$157.62	$157.60	$157.60
Purchase #5	$140.83	13.154%	$159.3548	$159.35	$159.35	$159.40
Purchase #6	$92.27	13.598%	$104.8169	$104.82	$104.80	$104.80
Purchase #7	$127.66	11.806%	$142.7315	$142.73	$142.75	$142.70
7 purchase totals =	$698.18		$782.2458	$782.24	$782.25	$782.10