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	$101.91	3.420%	$105.3953	$105.40	$105.40	$105.40
Purchase #2	$111.70	5.606%	$117.9619	$117.96	$117.95	$118.00
Purchase #3	$250.79	8.151%	$271.2319	$271.23	$271.25	$271.20
Purchase #4	$184.28	12.647%	$207.5859	$207.59	$207.60	$207.60
Purchase #5	$124.83	9.279%	$136.413	$136.41	$136.40	$136.40
Purchase #6	$39.57	6.208%	$42.0265	$42.03	$42.05	$42.00
Purchase #7	$178.35	10.411%	$196.918	$196.92	$196.90	$196.90
7 purchase totals =	$991.43		$1,077.5325	$1,077.54	$1,077.55	$1,077.50