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	$65.43	10.668%	$72.4101	$72.41	$72.40	$72.40
Purchase #2	$175.64	11.715%	$196.2162	$196.22	$196.20	$196.20
Purchase #3	$29.32	7.805%	$31.6084	$31.61	$31.60	$31.60
Purchase #4	$116.45	3.511%	$120.5386	$120.54	$120.55	$120.50
Purchase #5	$77.69	7.857%	$83.7941	$83.79	$83.80	$83.80
Purchase #6	$208.79	4.820%	$218.8537	$218.85	$218.85	$218.90
Purchase #7	$181.26	5.584%	$191.3816	$191.38	$191.40	$191.40
7 purchase totals =	$854.58		$914.8027	$914.80	$914.80	$914.80