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	$7.36	12.116%	$8.2517	$8.25	$8.25	$8.30
Purchase #2	$54.25	4.859%	$56.886	$56.89	$56.90	$56.90
Purchase #3	$192.40	13.754%	$218.8627	$218.86	$218.85	$218.90
Purchase #4	$90.59	8.647%	$98.4233	$98.42	$98.40	$98.40
Purchase #5	$167.81	7.606%	$180.5736	$180.57	$180.55	$180.60
Purchase #6	$83.82	7.252%	$89.8986	$89.90	$89.90	$89.90
Purchase #7	$231.26	11.827%	$258.6111	$258.61	$258.60	$258.60
7 purchase totals =	$827.49		$911.5070	$911.50	$911.45	$911.60