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	$41.56	6.216%	$44.1434	$44.14	$44.15	$44.10
Purchase #2	$242.72	10.528%	$268.2736	$268.27	$268.25	$268.30
Purchase #3	$109.52	9.397%	$119.8116	$119.81	$119.80	$119.80
Purchase #4	$41.64	9.374%	$45.5433	$45.54	$45.55	$45.50
Purchase #5	$90.34	7.466%	$97.0848	$97.08	$97.10	$97.10
Purchase #6	$41.96	3.654%	$43.4932	$43.49	$43.50	$43.50
Purchase #7	$178.47	4.833%	$187.0955	$187.10	$187.10	$187.10
7 purchase totals =	$746.21		$805.4454	$805.43	$805.45	$805.40