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	$72.71	7.536%	$78.1894	$78.19	$78.20	$78.20
Purchase #2	$27.30	7.137%	$29.2484	$29.25	$29.25	$29.20
Purchase #3	$154.94	7.233%	$166.1468	$166.15	$166.15	$166.10
Purchase #4	$156.89	9.316%	$171.5059	$171.51	$171.50	$171.50
Purchase #5	$232.81	12.342%	$261.5434	$261.54	$261.55	$261.50
Purchase #6	$55.80	5.416%	$58.8221	$58.82	$58.80	$58.80
Purchase #7	$164.37	3.695%	$170.4435	$170.44	$170.45	$170.40
7 purchase totals =	$864.82		$935.8995	$935.90	$935.90	$935.70