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	$121.81	9.848%	$133.8058	$133.81	$133.80	$133.80
Purchase #2	$101.69	12.250%	$114.147	$114.15	$114.15	$114.10
Purchase #3	$189.83	13.859%	$216.1385	$216.14	$216.15	$216.10
Purchase #4	$83.63	12.781%	$94.3188	$94.32	$94.30	$94.30
Purchase #5	$237.87	6.644%	$253.6741	$253.67	$253.65	$253.70
Purchase #6	$219.64	3.619%	$227.5888	$227.59	$227.60	$227.60
Purchase #7	$34.63	9.340%	$37.8644	$37.86	$37.85	$37.90
7 purchase totals =	$989.10		$1,077.5374	$1,077.54	$1,077.50	$1,077.50