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	$159.85	3.309%	$165.1394	$165.14	$165.15	$165.10
Purchase #2	$39.75	9.611%	$43.5704	$43.57	$43.55	$43.60
Purchase #3	$160.88	12.757%	$181.4035	$181.40	$181.40	$181.40
Purchase #4	$158.55	11.299%	$176.4646	$176.46	$176.45	$176.50
Purchase #5	$122.27	11.862%	$136.7737	$136.77	$136.75	$136.80
Purchase #6	$123.79	12.199%	$138.8911	$138.89	$138.90	$138.90
Purchase #7	$53.52	11.694%	$59.7786	$59.78	$59.80	$59.80
7 purchase totals =	$818.61		$902.0213	$902.01	$902.00	$902.10