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	$36.48	3.416%	$37.7262	$37.73	$37.75	$37.70
Purchase #2	$56.39	10.581%	$62.3566	$62.36	$62.35	$62.40
Purchase #3	$37.89	12.817%	$42.7464	$42.75	$42.75	$42.70
Purchase #4	$63.65	13.226%	$72.0683	$72.07	$72.05	$72.10
Purchase #5	$75.62	5.240%	$79.5825	$79.58	$79.60	$79.60
Purchase #6	$186.29	13.194%	$210.8691	$210.87	$210.85	$210.90
Purchase #7	$178.45	9.116%	$194.7175	$194.72	$194.70	$194.70
7 purchase totals =	$634.77		$700.0666	$700.08	$700.05	$700.10