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	$172.34	8.599%	$187.1595	$187.16	$187.15	$187.20
Purchase #2	$78.46	10.666%	$86.8285	$86.83	$86.85	$86.80
Purchase #3	$158.61	3.604%	$164.3263	$164.33	$164.35	$164.30
Purchase #4	$48.81	9.340%	$53.3689	$53.37	$53.35	$53.40
Purchase #5	$140.45	9.175%	$153.3363	$153.34	$153.35	$153.30
Purchase #6	$239.78	3.375%	$247.8726	$247.87	$247.85	$247.90
Purchase #7	$231.43	13.133%	$261.8237	$261.82	$261.80	$261.80
7 purchase totals =	$1,069.88		$1,154.7158	$1,154.72	$1,154.70	$1,154.70