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	$48.88	5.126%	$51.3856	$51.39	$51.40	$51.40
Purchase #2	$51.33	7.555%	$55.208	$55.21	$55.20	$55.20
Purchase #3	$47.38	10.415%	$52.3146	$52.31	$52.30	$52.30
Purchase #4	$91.71	11.477%	$102.2356	$102.24	$102.25	$102.20
Purchase #5	$56.32	6.331%	$59.8856	$59.89	$59.90	$59.90
Purchase #6	$34.31	11.697%	$38.3232	$38.32	$38.30	$38.30
Purchase #7	$49.84	3.633%	$51.6507	$51.65	$51.65	$51.70
7 purchase totals =	$379.77		$411.0033	$411.01	$411.00	$411.00