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	$89.44	9.737%	$98.1488	$98.15	$98.15	$98.10
Purchase #2	$19.45	8.469%	$21.0972	$21.10	$21.10	$21.10
Purchase #3	$181.82	4.823%	$190.5892	$190.59	$190.60	$190.60
Purchase #4	$194.26	12.342%	$218.2356	$218.24	$218.25	$218.20
Purchase #5	$28.37	9.819%	$31.1557	$31.16	$31.15	$31.20
Purchase #6	$165.57	11.563%	$184.7149	$184.71	$184.70	$184.70
Purchase #7	$102.59	10.608%	$113.4727	$113.47	$113.45	$113.50
7 purchase totals =	$781.50		$857.4141	$857.42	$857.40	$857.40