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	$76.43	7.317%	$82.0224	$82.02	$82.00	$82.00
Purchase #2	$131.75	7.241%	$141.29	$141.29	$141.30	$141.30
Purchase #3	$156.46	4.816%	$163.9951	$164.00	$164.00	$164.00
Purchase #4	$18.82	7.504%	$20.2323	$20.23	$20.25	$20.20
Purchase #5	$72.79	10.156%	$80.1826	$80.18	$80.20	$80.20
Purchase #6	$18.66	7.373%	$20.0358	$20.04	$20.05	$20.00
Purchase #7	$243.85	10.650%	$269.82	$269.82	$269.80	$269.80
7 purchase totals =	$718.76		$777.5782	$777.58	$777.60	$777.50