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	$127.30	9.202%	$139.0141	$139.01	$139.00	$139.00
Purchase #2	$151.60	4.527%	$158.4629	$158.46	$158.45	$158.50
Purchase #3	$89.98	10.641%	$99.5548	$99.55	$99.55	$99.60
Purchase #4	$47.88	5.666%	$50.5929	$50.59	$50.60	$50.60
Purchase #5	$197.64	5.371%	$208.2552	$208.26	$208.25	$208.30
Purchase #6	$104.61	10.804%	$115.9121	$115.91	$115.90	$115.90
Purchase #7	$239.82	10.795%	$265.7086	$265.71	$265.70	$265.70
7 purchase totals =	$958.83		$1,037.5006	$1,037.49	$1,037.45	$1,037.60