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	$135.46	6.678%	$144.506	$144.51	$144.50	$144.50
Purchase #2	$30.95	8.584%	$33.6067	$33.61	$33.60	$33.60
Purchase #3	$123.83	10.192%	$136.4508	$136.45	$136.45	$136.50
Purchase #4	$223.83	8.697%	$243.2965	$243.30	$243.30	$243.30
Purchase #5	$141.91	10.543%	$156.8716	$156.87	$156.85	$156.90
Purchase #6	$211.71	6.481%	$225.4309	$225.43	$225.45	$225.40
Purchase #7	$183.29	13.740%	$208.474	$208.47	$208.45	$208.50
7 purchase totals =	$1,050.98		$1,148.6365	$1,148.64	$1,148.60	$1,148.70