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	$101.83	13.493%	$115.5699	$115.57	$115.55	$115.60
Purchase #2	$100.40	3.596%	$104.0104	$104.01	$104.00	$104.00
Purchase #3	$141.60	10.519%	$156.4949	$156.49	$156.50	$156.50
Purchase #4	$189.89	7.761%	$204.6274	$204.63	$204.65	$204.60
Purchase #5	$240.58	4.478%	$251.3532	$251.35	$251.35	$251.40
Purchase #6	$174.89	9.154%	$190.8994	$190.90	$190.90	$190.90
Purchase #7	$63.53	11.126%	$70.5983	$70.60	$70.60	$70.60
7 purchase totals =	$1,012.72		$1,093.5535	$1,093.55	$1,093.55	$1,093.60