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	$243.84	12.517%	$274.3615	$274.36	$274.35	$274.40
Purchase #2	$20.74	13.746%	$23.5909	$23.59	$23.60	$23.60
Purchase #3	$65.50	8.626%	$71.15	$71.15	$71.15	$71.20
Purchase #4	$77.96	12.410%	$87.6348	$87.63	$87.65	$87.60
Purchase #5	$210.48	11.135%	$233.9169	$233.92	$233.90	$233.90
Purchase #6	$200.84	4.789%	$210.4582	$210.46	$210.45	$210.50
Purchase #7	$91.87	12.450%	$103.3078	$103.31	$103.30	$103.30
7 purchase totals =	$911.23		$1,004.4201	$1,004.42	$1,004.40	$1,004.50