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	$42.93	6.350%	$45.6561	$45.66	$45.65	$45.70
Purchase #2	$117.33	9.840%	$128.8753	$128.88	$128.90	$128.90
Purchase #3	$238.27	13.734%	$270.994	$270.99	$271.00	$271.00
Purchase #4	$38.89	3.451%	$40.2321	$40.23	$40.25	$40.20
Purchase #5	$232.47	12.128%	$260.664	$260.66	$260.65	$260.70
Purchase #6	$196.85	13.703%	$223.8244	$223.82	$223.80	$223.80
Purchase #7	$185.78	13.798%	$211.4139	$211.41	$211.40	$211.40
7 purchase totals =	$1,052.52		$1,181.6598	$1,181.65	$1,181.65	$1,181.70