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	$37.45	13.333%	$42.4432	$42.44	$42.45	$42.40
Purchase #2	$77.86	8.723%	$84.6517	$84.65	$84.65	$84.70
Purchase #3	$58.59	6.610%	$62.4628	$62.46	$62.45	$62.50
Purchase #4	$96.78	6.813%	$103.3736	$103.37	$103.35	$103.40
Purchase #5	$42.52	7.176%	$45.5712	$45.57	$45.55	$45.60
Purchase #6	$224.45	6.624%	$239.3176	$239.32	$239.30	$239.30
Purchase #7	$138.65	4.149%	$144.4026	$144.40	$144.40	$144.40
7 purchase totals =	$676.30		$722.2227	$722.21	$722.15	$722.30