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	$6.88	10.473%	$7.6005	$7.60	$7.60	$7.60
Purchase #2	$59.40	12.801%	$67.0038	$67.00	$67.00	$67.00
Purchase #3	$41.34	7.483%	$44.4335	$44.43	$44.45	$44.40
Purchase #4	$189.84	5.609%	$200.4881	$200.49	$200.50	$200.50
Purchase #5	$39.60	9.474%	$43.3517	$43.35	$43.35	$43.40
Purchase #6	$76.72	12.236%	$86.1075	$86.11	$86.10	$86.10
Purchase #7	$173.60	6.613%	$185.0802	$185.08	$185.10	$185.10
7 purchase totals =	$587.38		$634.0653	$634.06	$634.10	$634.10