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	$178.47	12.316%	$200.4504	$200.45	$200.45	$200.50
Purchase #2	$61.55	9.549%	$67.4274	$67.43	$67.45	$67.40
Purchase #3	$97.27	8.556%	$105.5924	$105.59	$105.60	$105.60
Purchase #4	$37.83	13.761%	$43.0358	$43.04	$43.05	$43.00
Purchase #5	$140.58	5.232%	$147.9351	$147.94	$147.95	$147.90
Purchase #6	$96.83	5.315%	$101.9765	$101.98	$102.00	$102.00
Purchase #7	$208.61	12.326%	$234.3233	$234.32	$234.30	$234.30
7 purchase totals =	$821.14		$900.7409	$900.75	$900.80	$900.70