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	$51.49	7.576%	$55.3909	$55.39	$55.40	$55.40
Purchase #2	$84.77	6.308%	$90.1173	$90.12	$90.10	$90.10
Purchase #3	$238.79	10.241%	$263.2445	$263.24	$263.25	$263.20
Purchase #4	$197.27	4.868%	$206.8731	$206.87	$206.85	$206.90
Purchase #5	$67.52	4.362%	$70.4652	$70.47	$70.45	$70.50
Purchase #6	$173.40	9.318%	$189.5574	$189.56	$189.55	$189.60
Purchase #7	$151.87	8.299%	$164.4737	$164.47	$164.45	$164.50
7 purchase totals =	$965.11		$1,040.1221	$1,040.12	$1,040.05	$1,040.20