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	$120.91	4.470%	$126.3147	$126.31	$126.30	$126.30
Purchase #2	$188.45	12.209%	$211.4579	$211.46	$211.45	$211.50
Purchase #3	$52.86	6.329%	$56.2055	$56.21	$56.20	$56.20
Purchase #4	$87.73	3.393%	$90.7067	$90.71	$90.70	$90.70
Purchase #5	$128.70	12.717%	$145.0668	$145.07	$145.05	$145.10
Purchase #6	$130.51	8.828%	$142.0314	$142.03	$142.05	$142.00
Purchase #7	$76.62	4.587%	$80.1346	$80.13	$80.15	$80.10
7 purchase totals =	$785.78		$851.9176	$851.92	$851.90	$851.90