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	$85.48	6.331%	$90.8917	$90.89	$90.90	$90.90
Purchase #2	$214.97	8.597%	$233.451	$233.45	$233.45	$233.50
Purchase #3	$80.86	11.445%	$90.1144	$90.11	$90.10	$90.10
Purchase #4	$201.86	3.332%	$208.586	$208.59	$208.60	$208.60
Purchase #5	$161.57	3.582%	$167.3574	$167.36	$167.35	$167.40
Purchase #6	$55.72	13.433%	$63.2049	$63.20	$63.20	$63.20
Purchase #7	$52.63	3.603%	$54.5263	$54.53	$54.55	$54.50
7 purchase totals =	$853.09		$908.1317	$908.13	$908.15	$908.20