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	$51.82	9.780%	$56.888	$56.89	$56.90	$56.90
Purchase #2	$44.38	3.217%	$45.8077	$45.81	$45.80	$45.80
Purchase #3	$61.34	12.691%	$69.1247	$69.12	$69.10	$69.10
Purchase #4	$180.32	9.176%	$196.8662	$196.87	$196.85	$196.90
Purchase #5	$72.48	12.262%	$81.3675	$81.37	$81.35	$81.40
Purchase #6	$138.86	9.251%	$151.7059	$151.71	$151.70	$151.70
Purchase #7	$163.90	4.726%	$171.6459	$171.65	$171.65	$171.60
7 purchase totals =	$713.10		$773.4059	$773.42	$773.35	$773.40