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	$128.72	4.848%	$134.9603	$134.96	$134.95	$135.00
Purchase #2	$40.46	4.611%	$42.3256	$42.33	$42.35	$42.30
Purchase #3	$46.54	6.158%	$49.4059	$49.41	$49.40	$49.40
Purchase #4	$194.93	7.456%	$209.464	$209.46	$209.45	$209.50
Purchase #5	$34.89	8.724%	$37.9338	$37.93	$37.95	$37.90
Purchase #6	$66.86	8.203%	$72.3445	$72.34	$72.35	$72.30
Purchase #7	$207.72	10.703%	$229.9523	$229.95	$229.95	$230.00
7 purchase totals =	$720.12		$776.3864	$776.38	$776.40	$776.40