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	$38.77	4.135%	$40.3731	$40.37	$40.35	$40.40
Purchase #2	$198.40	12.467%	$223.1345	$223.13	$223.15	$223.10
Purchase #3	$243.97	9.832%	$267.9571	$267.96	$267.95	$268.00
Purchase #4	$25.39	9.154%	$27.7142	$27.71	$27.70	$27.70
Purchase #5	$151.69	10.450%	$167.5416	$167.54	$167.55	$167.50
Purchase #6	$179.64	5.363%	$189.2741	$189.27	$189.25	$189.30
Purchase #7	$177.70	12.719%	$200.3017	$200.30	$200.30	$200.30
7 purchase totals =	$1,015.56		$1,116.2963	$1,116.28	$1,116.25	$1,116.30