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	$213.51	11.721%	$238.5355	$238.54	$238.55	$238.50
Purchase #2	$212.71	12.232%	$238.7287	$238.73	$238.75	$238.70
Purchase #3	$208.33	12.139%	$233.6192	$233.62	$233.60	$233.60
Purchase #4	$73.57	9.825%	$80.7983	$80.80	$80.80	$80.80
Purchase #5	$189.33	4.194%	$197.2705	$197.27	$197.25	$197.30
Purchase #6	$140.34	4.703%	$146.9402	$146.94	$146.95	$146.90
Purchase #7	$101.25	9.744%	$111.1158	$111.12	$111.10	$111.10
7 purchase totals =	$1,139.04		$1,247.0082	$1,247.02	$1,247.00	$1,246.90