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	$27.66	4.871%	$29.0073	$29.01	$29.00	$29.00
Purchase #2	$37.60	13.180%	$42.5557	$42.56	$42.55	$42.60
Purchase #3	$117.56	12.206%	$131.9094	$131.91	$131.90	$131.90
Purchase #4	$107.45	3.108%	$110.7895	$110.79	$110.80	$110.80
Purchase #5	$7.51	4.693%	$7.8624	$7.86	$7.85	$7.90
Purchase #6	$75.26	3.270%	$77.721	$77.72	$77.70	$77.70
Purchase #7	$161.52	9.450%	$176.7836	$176.78	$176.80	$176.80
7 purchase totals =	$534.56		$576.6289	$576.63	$576.60	$576.70