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	$111.88	5.583%	$118.1263	$118.13	$118.15	$118.10
Purchase #2	$73.77	5.413%	$77.7632	$77.76	$77.75	$77.80
Purchase #3	$116.46	6.483%	$124.0101	$124.01	$124.00	$124.00
Purchase #4	$80.27	13.161%	$90.8343	$90.83	$90.85	$90.80
Purchase #5	$13.65	12.621%	$15.3728	$15.37	$15.35	$15.40
Purchase #6	$152.40	12.508%	$171.4622	$171.46	$171.45	$171.50
Purchase #7	$39.32	12.497%	$44.2338	$44.23	$44.25	$44.20
7 purchase totals =	$587.75		$641.8027	$641.79	$641.80	$641.80