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	$139.88	13.371%	$158.5834	$158.58	$158.60	$158.60
Purchase #2	$39.85	4.399%	$41.603	$41.60	$41.60	$41.60
Purchase #3	$94.44	5.385%	$99.5256	$99.53	$99.55	$99.50
Purchase #4	$164.48	3.143%	$169.6496	$169.65	$169.65	$169.60
Purchase #5	$57.96	8.394%	$62.8252	$62.83	$62.85	$62.80
Purchase #6	$122.41	8.635%	$132.9801	$132.98	$133.00	$133.00
Purchase #7	$55.71	13.753%	$63.3718	$63.37	$63.35	$63.40
7 purchase totals =	$674.73		$728.5387	$728.54	$728.60	$728.50