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	$242.53	12.805%	$273.586	$273.59	$273.60	$273.60
Purchase #2	$212.96	6.621%	$227.0601	$227.06	$227.05	$227.10
Purchase #3	$24.45	12.735%	$27.5637	$27.56	$27.55	$27.60
Purchase #4	$159.70	7.530%	$171.7254	$171.73	$171.75	$171.70
Purchase #5	$83.86	10.569%	$92.7232	$92.72	$92.70	$92.70
Purchase #6	$203.70	8.462%	$220.9371	$220.94	$220.95	$220.90
Purchase #7	$82.50	5.447%	$86.9938	$86.99	$87.00	$87.00
7 purchase totals =	$1,009.70		$1,100.5893	$1,100.59	$1,100.60	$1,100.60