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	$126.40	12.563%	$142.2796	$142.28	$142.30	$142.30
Purchase #2	$226.88	5.238%	$238.764	$238.76	$238.75	$238.80
Purchase #3	$117.40	11.848%	$131.3096	$131.31	$131.30	$131.30
Purchase #4	$61.77	7.628%	$66.4818	$66.48	$66.50	$66.50
Purchase #5	$94.54	3.481%	$97.8309	$97.83	$97.85	$97.80
Purchase #6	$179.38	8.458%	$194.552	$194.55	$194.55	$194.60
Purchase #7	$56.40	9.775%	$61.9131	$61.91	$61.90	$61.90
7 purchase totals =	$862.77		$933.1310	$933.12	$933.15	$933.20