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	$29.41	7.632%	$31.6546	$31.65	$31.65	$31.70
Purchase #2	$26.91	3.607%	$27.8806	$27.88	$27.90	$27.90
Purchase #3	$229.52	6.249%	$243.8627	$243.86	$243.85	$243.90
Purchase #4	$181.53	10.669%	$200.8974	$200.90	$200.90	$200.90
Purchase #5	$218.42	9.522%	$239.218	$239.22	$239.20	$239.20
Purchase #6	$173.58	4.843%	$181.9865	$181.99	$182.00	$182.00
Purchase #7	$166.85	4.563%	$174.4634	$174.46	$174.45	$174.50
7 purchase totals =	$1,026.22		$1,099.9632	$1,099.96	$1,099.95	$1,100.10