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	$243.69	6.213%	$258.8305	$258.83	$258.85	$258.80
Purchase #2	$218.66	4.417%	$228.3182	$228.32	$228.30	$228.30
Purchase #3	$213.47	4.276%	$222.598	$222.60	$222.60	$222.60
Purchase #4	$47.32	8.167%	$51.1846	$51.18	$51.20	$51.20
Purchase #5	$72.96	4.667%	$76.365	$76.37	$76.35	$76.40
Purchase #6	$239.57	3.558%	$248.0939	$248.09	$248.10	$248.10
Purchase #7	$34.98	9.159%	$38.1838	$38.18	$38.20	$38.20
7 purchase totals =	$1,070.65		$1,123.5740	$1,123.57	$1,123.60	$1,123.60