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	$122.55	12.109%	$137.3896	$137.39	$137.40	$137.40
Purchase #2	$189.81	13.839%	$216.0778	$216.08	$216.10	$216.10
Purchase #3	$63.71	13.807%	$72.5064	$72.51	$72.50	$72.50
Purchase #4	$148.61	12.292%	$166.8771	$166.88	$166.90	$166.90
Purchase #5	$12.98	6.360%	$13.8055	$13.81	$13.80	$13.80
Purchase #6	$206.30	9.788%	$226.4926	$226.49	$226.50	$226.50
Purchase #7	$149.55	13.563%	$169.8335	$169.83	$169.85	$169.80
7 purchase totals =	$893.51		$1,002.9825	$1,002.99	$1,003.05	$1,003.00