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	$112.97	5.329%	$118.9902	$118.99	$119.00	$119.00
Purchase #2	$39.26	10.566%	$43.4082	$43.41	$43.40	$43.40
Purchase #3	$56.52	10.464%	$62.4343	$62.43	$62.45	$62.40
Purchase #4	$134.55	5.541%	$142.0054	$142.01	$142.00	$142.00
Purchase #5	$47.96	12.868%	$54.1315	$54.13	$54.15	$54.10
Purchase #6	$124.31	12.234%	$139.5181	$139.52	$139.50	$139.50
Purchase #7	$100.90	5.554%	$106.504	$106.50	$106.50	$106.50
7 purchase totals =	$616.47		$666.9917	$666.99	$667.00	$666.90