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	$58.78	6.368%	$62.5231	$62.52	$62.50	$62.50
Purchase #2	$146.89	3.385%	$151.8622	$151.86	$151.85	$151.90
Purchase #3	$131.41	10.828%	$145.6391	$145.64	$145.65	$145.60
Purchase #4	$24.64	7.740%	$26.5471	$26.55	$26.55	$26.50
Purchase #5	$157.47	4.175%	$164.0444	$164.04	$164.05	$164.00
Purchase #6	$28.30	9.816%	$31.0779	$31.08	$31.10	$31.10
Purchase #7	$177.78	4.866%	$186.4308	$186.43	$186.45	$186.40
7 purchase totals =	$725.27		$768.1246	$768.12	$768.15	$768.00