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	$245.58	8.783%	$267.1493	$267.15	$267.15	$267.10
Purchase #2	$155.30	6.308%	$165.0963	$165.10	$165.10	$165.10
Purchase #3	$54.48	12.779%	$61.442	$61.44	$61.45	$61.40
Purchase #4	$164.95	4.469%	$172.3216	$172.32	$172.30	$172.30
Purchase #5	$148.37	4.328%	$154.7915	$154.79	$154.80	$154.80
Purchase #6	$198.70	12.179%	$222.8997	$222.90	$222.90	$222.90
Purchase #7	$197.82	7.800%	$213.25	$213.25	$213.25	$213.30
7 purchase totals =	$1,165.20		$1,256.9504	$1,256.95	$1,256.95	$1,256.90