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	$219.77	13.641%	$249.7488	$249.75	$249.75	$249.70
Purchase #2	$62.79	5.710%	$66.3753	$66.38	$66.40	$66.40
Purchase #3	$137.40	3.865%	$142.7105	$142.71	$142.70	$142.70
Purchase #4	$102.66	10.148%	$113.0779	$113.08	$113.10	$113.10
Purchase #5	$73.65	6.276%	$78.2723	$78.27	$78.25	$78.30
Purchase #6	$39.89	8.175%	$43.151	$43.15	$43.15	$43.20
Purchase #7	$68.86	12.434%	$77.4221	$77.42	$77.40	$77.40
7 purchase totals =	$705.02		$770.7579	$770.76	$770.75	$770.80