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	$33.44	6.202%	$35.5139	$35.51	$35.50	$35.50
Purchase #2	$138.85	9.326%	$151.7992	$151.80	$151.80	$151.80
Purchase #3	$151.32	7.360%	$162.4572	$162.46	$162.45	$162.50
Purchase #4	$46.76	6.773%	$49.9271	$49.93	$49.95	$49.90
Purchase #5	$89.48	11.580%	$99.8418	$99.84	$99.85	$99.80
Purchase #6	$221.64	4.605%	$231.8465	$231.85	$231.85	$231.80
Purchase #7	$121.61	7.825%	$131.126	$131.13	$131.15	$131.10
7 purchase totals =	$803.10		$862.5117	$862.52	$862.55	$862.40