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	$26.33	4.110%	$27.4122	$27.41	$27.40	$27.40
Purchase #2	$42.94	5.477%	$45.2918	$45.29	$45.30	$45.30
Purchase #3	$60.27	13.727%	$68.5433	$68.54	$68.55	$68.50
Purchase #4	$161.69	11.628%	$180.4913	$180.49	$180.50	$180.50
Purchase #5	$91.62	9.726%	$100.531	$100.53	$100.55	$100.50
Purchase #6	$38.32	6.830%	$40.9373	$40.94	$40.95	$40.90
Purchase #7	$66.91	5.320%	$70.4696	$70.47	$70.45	$70.50
7 purchase totals =	$488.08		$533.6765	$533.67	$533.70	$533.60