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	$128.72	10.589%	$142.3502	$142.35	$142.35	$142.40
Purchase #2	$144.84	13.815%	$164.8496	$164.85	$164.85	$164.80
Purchase #3	$105.33	8.667%	$114.459	$114.46	$114.45	$114.50
Purchase #4	$36.52	9.183%	$39.8736	$39.87	$39.85	$39.90
Purchase #5	$210.55	8.728%	$228.9268	$228.93	$228.95	$228.90
Purchase #6	$6.98	13.664%	$7.9337	$7.93	$7.95	$7.90
Purchase #7	$172.56	12.338%	$193.8505	$193.85	$193.85	$193.90
7 purchase totals =	$805.50		$892.2434	$892.24	$892.25	$892.30