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	$10.73	10.852%	$11.8944	$11.89	$11.90	$11.90
Purchase #2	$179.77	9.506%	$196.8589	$196.86	$196.85	$196.90
Purchase #3	$189.31	12.786%	$213.5152	$213.52	$213.50	$213.50
Purchase #4	$229.42	3.161%	$236.672	$236.67	$236.65	$236.70
Purchase #5	$136.82	8.765%	$148.8123	$148.81	$148.80	$148.80
Purchase #6	$171.67	7.387%	$184.3513	$184.35	$184.35	$184.40
Purchase #7	$188.28	4.139%	$196.0729	$196.07	$196.05	$196.10
7 purchase totals =	$1,106.00		$1,188.1770	$1,188.17	$1,188.10	$1,188.30