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	$18.49	12.611%	$20.8218	$20.82	$20.80	$20.80
Purchase #2	$46.95	9.195%	$51.2671	$51.27	$51.25	$51.30
Purchase #3	$184.85	13.745%	$210.2576	$210.26	$210.25	$210.30
Purchase #4	$98.60	13.240%	$111.6546	$111.65	$111.65	$111.70
Purchase #5	$250.47	4.592%	$261.9716	$261.97	$261.95	$262.00
Purchase #6	$197.65	12.793%	$222.9354	$222.94	$222.95	$222.90
Purchase #7	$218.99	4.870%	$229.6548	$229.65	$229.65	$229.70
7 purchase totals =	$1,016.00		$1,108.5629	$1,108.56	$1,108.50	$1,108.70