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	$131.91	3.664%	$136.7432	$136.74	$136.75	$136.70
Purchase #2	$111.68	3.772%	$115.8926	$115.89	$115.90	$115.90
Purchase #3	$141.60	9.451%	$154.9826	$154.98	$155.00	$155.00
Purchase #4	$215.89	4.305%	$225.1841	$225.18	$225.20	$225.20
Purchase #5	$142.49	7.192%	$152.7379	$152.74	$152.75	$152.70
Purchase #6	$82.63	9.467%	$90.4526	$90.45	$90.45	$90.50
Purchase #7	$161.38	9.625%	$176.9128	$176.91	$176.90	$176.90
7 purchase totals =	$987.58		$1,052.9058	$1,052.89	$1,052.95	$1,052.90