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	$228.34	12.188%	$256.1701	$256.17	$256.15	$256.20
Purchase #2	$172.96	13.360%	$196.0675	$196.07	$196.05	$196.10
Purchase #3	$184.51	8.699%	$200.5605	$200.56	$200.55	$200.60
Purchase #4	$42.29	3.553%	$43.7926	$43.79	$43.80	$43.80
Purchase #5	$147.91	10.686%	$163.7157	$163.72	$163.70	$163.70
Purchase #6	$180.64	5.666%	$190.8751	$190.88	$190.90	$190.90
Purchase #7	$224.99	6.292%	$239.1464	$239.15	$239.15	$239.10
7 purchase totals =	$1,181.64		$1,290.3279	$1,290.34	$1,290.30	$1,290.40