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	$130.40	6.249%	$138.5487	$138.55	$138.55	$138.50
Purchase #2	$161.96	6.548%	$172.5651	$172.57	$172.55	$172.60
Purchase #3	$108.58	10.566%	$120.0526	$120.05	$120.05	$120.10
Purchase #4	$139.91	8.371%	$151.6219	$151.62	$151.60	$151.60
Purchase #5	$103.46	8.517%	$112.2717	$112.27	$112.25	$112.30
Purchase #6	$103.73	7.767%	$111.7867	$111.79	$111.80	$111.80
Purchase #7	$39.34	13.676%	$44.7201	$44.72	$44.70	$44.70
7 purchase totals =	$787.38		$851.5668	$851.57	$851.50	$851.60