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	$50.72	3.474%	$52.482	$52.48	$52.50	$52.50
Purchase #2	$222.67	3.444%	$230.3388	$230.34	$230.35	$230.30
Purchase #3	$39.25	12.602%	$44.1963	$44.20	$44.20	$44.20
Purchase #4	$242.79	6.846%	$259.4114	$259.41	$259.40	$259.40
Purchase #5	$77.65	3.624%	$80.464	$80.46	$80.45	$80.50
Purchase #6	$73.90	11.667%	$82.5219	$82.52	$82.50	$82.50
Purchase #7	$87.83	5.853%	$92.9707	$92.97	$92.95	$93.00
7 purchase totals =	$794.81		$842.3851	$842.38	$842.35	$842.40