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	$36.52	7.871%	$39.3945	$39.39	$39.40	$39.40
Purchase #2	$156.71	10.633%	$173.373	$173.37	$173.35	$173.40
Purchase #3	$171.96	4.573%	$179.8237	$179.82	$179.80	$179.80
Purchase #4	$93.27	9.727%	$102.3424	$102.34	$102.35	$102.30
Purchase #5	$61.25	7.393%	$65.7782	$65.78	$65.80	$65.80
Purchase #6	$200.83	6.128%	$213.1369	$213.14	$213.15	$213.10
Purchase #7	$235.86	11.192%	$262.2575	$262.26	$262.25	$262.30
7 purchase totals =	$956.40		$1,036.1062	$1,036.10	$1,036.10	$1,036.10