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	$52.77	8.112%	$57.0507	$57.05	$57.05	$57.10
Purchase #2	$228.30	11.706%	$255.0248	$255.02	$255.00	$255.00
Purchase #3	$101.61	13.766%	$115.5976	$115.60	$115.60	$115.60
Purchase #4	$226.31	3.254%	$233.6741	$233.67	$233.65	$233.70
Purchase #5	$72.32	8.576%	$78.5222	$78.52	$78.50	$78.50
Purchase #6	$246.65	4.802%	$258.4941	$258.49	$258.50	$258.50
Purchase #7	$221.86	12.857%	$250.3845	$250.38	$250.40	$250.40
7 purchase totals =	$1,149.82		$1,248.7480	$1,248.73	$1,248.70	$1,248.80