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	$38.31	12.643%	$43.1535	$43.15	$43.15	$43.20
Purchase #2	$164.87	12.283%	$185.121	$185.12	$185.10	$185.10
Purchase #3	$18.99	7.153%	$20.3484	$20.35	$20.35	$20.30
Purchase #4	$97.33	5.266%	$102.4554	$102.46	$102.45	$102.50
Purchase #5	$73.38	4.250%	$76.4987	$76.50	$76.50	$76.50
Purchase #6	$237.25	7.819%	$255.8006	$255.80	$255.80	$255.80
Purchase #7	$204.64	5.543%	$215.9832	$215.98	$216.00	$216.00
7 purchase totals =	$834.77		$899.3608	$899.36	$899.35	$899.40