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	$77.47	4.371%	$80.8562	$80.86	$80.85	$80.90
Purchase #2	$18.74	13.769%	$21.3203	$21.32	$21.30	$21.30
Purchase #3	$73.88	6.399%	$78.6076	$78.61	$78.60	$78.60
Purchase #4	$52.37	3.367%	$54.1333	$54.13	$54.15	$54.10
Purchase #5	$131.94	4.750%	$138.2072	$138.21	$138.20	$138.20
Purchase #6	$206.55	6.634%	$220.2525	$220.25	$220.25	$220.30
Purchase #7	$51.78	5.274%	$54.5109	$54.51	$54.50	$54.50
7 purchase totals =	$612.73		$647.8880	$647.89	$647.85	$647.90