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	$27.97	5.588%	$29.533	$29.53	$29.55	$29.50
Purchase #2	$225.66	13.619%	$256.3926	$256.39	$256.40	$256.40
Purchase #3	$136.62	6.553%	$145.5727	$145.57	$145.55	$145.60
Purchase #4	$69.49	12.388%	$78.0984	$78.10	$78.10	$78.10
Purchase #5	$110.29	7.249%	$118.2849	$118.28	$118.30	$118.30
Purchase #6	$77.91	11.244%	$86.6702	$86.67	$86.65	$86.70
Purchase #7	$151.47	12.170%	$169.9039	$169.90	$169.90	$169.90
7 purchase totals =	$799.41		$884.4557	$884.44	$884.45	$884.50